It should have been Georges St-Pierre against Nick Diaz.  Right?

Or was it GSP against Carlos Condit?

Well, now we’ve come full circle, with Diaz in the main event, but against B.J. Penn rather than the current UFC welterweight champion.

Despite all of the changes to the main event of Saturday’s UFC 137 event, which takes place at the Mandalay Bay Events Center in Las Vegas, there’s still an immense amount of interest in the two men atop the card.  Some might even argue that the new main event is better than either of the prior options.

Diaz will make his return to the Octagon following a dominant run as the Strikeforce welterweight champion.  That alone makes for an intriguing storyline.  While there’s no denying that the bad boy from Stockton had built a strong fan base in his previous run with the organization despite only compiling a 6-4 record, his success since leaving the UFC adds a whole new dimension to his return.  While he left as a popular fighter with a strong personality, he returns as a top contender.

He also returns amid controversy, missing media appearances to the point of being yanked from a title shot against GSP and inserted into a bout with Penn.  Penn would like to make a statement and somehow renew interest in another meeting between him and St-Pierre.  Diaz, meanwhile, is out to prove that his run in Strikeforce can translate into success in the UFC Octagon.

The bout tops a card that also includes two heavyweight match-ups. Matt Mitrione continues to face increasingly tough competition, this time in the form of Cheick Kongo, while Mirko “Cro Cop” Filipovic looks to rebound from a two-fight skid when he meets Roy Nelson.  Rounding out the main card, which airs live on pay-per-view at 9 p.m. ET, George Roop welcomes top-5 featherweight Hatsu Hioki into the UFC and bantamweight Jeff Curran returns to the Octagon after nearly eight years to battle Scott Jorgensen.

The MMA Corner panel of Corey Adams, Brian McKenna and Richard Wilcoxon share their thoughts on all five main card bouts in this edition of the Round Table.

BW: Scott Jorgensen (12-4) vs. Jeff Curran (33-13-1)

McKenna: At 34-years-old, Jeff Curran will make his return to the UFC this Saturday. His first stint with the promotion came at UFC 46 where he lost by unanimous decision to Matt Serra. Since then, he has gone on to fight with Pride, WEC, Strikeforce, Bellator and a bunch of minor promotions. That has been the story of his career, as Curran has always been good, but not great. He has elite jiu-jitsu skills, which has landed him a second-degree black belt, but his striking has never been anything special. It is really clear when you look at his record and see that of his 33 victories, 19 have come by submission and only one has come by knockout.

Scott Jorgensen (Tracy Lee/Combat Lifestyle)

Across the cage from Curran will stand Scott Jorgensen, who is one of the top bantamweights in the world. Before he lost to Dominick Cruz for the title on the final WEC card, Jorgensen was on a five-fight winning streak. After the loss, he took on Ken Stone and even though Stone was controlling the fight early, “Young Guns” turned the tide when he knocked out Stone from his guard. Rarely you see a fighter knock someone out from that position that early in the fight, but it goes to show you the power that he has behind his fists. People know him as a wrestler, considering his background and his association with Team Alpha Male, but people also need to respect that power.

It is a shame that Curran’s first fight back with the top promotion in the world is going to be against such a good fighter. It would have been great to see the jiu-jitsu ace showcase his skills, but I would be surprised if we saw this fight go to the ground. Knowing the holes that Curran has in his striking, Jorgensen will use his power and achieve the TKO sometime in the second round.

Wilcoxon: Curran is on of those old-time fighters. He is a guy who fought at lightweight because most promotions didn’t offer his weight class. Now at age 34, he is getting long at the tooth. His body has been battered and he isn’t the fighter he used to be.

Jeff Curran (Keith Mills/Sherdog)

While Curran used to be one of he best little men around, Jorgensen is one of the best today. His wrestling background, submission defense and power all tilt this fight in his favor. I look for Jorgensen to dominate the battle. But Curran has been to the judges’ scorecards in seven of his last eight fights and I think he lasts to the end in this one as well.

Adams: Brian did a solid job laying this match-up out, as Curran will try to stop Jorgensen, but I also don’t believe that will happen.

Curran hasn’t fought on a major stage since August 2009 during his stint with the WEC. He has won three fights with XFO in the past couple of years, but the competition level is far from what Jorgensen brings to the table.

Yes, the majority of Curran’s fights have gone to decision, but look at the man standing on the opposite side of the cage: “Young Guns.” Jorgensen had never showed much knockout power in the past, but against Stone, he made it clear that his MMA game is evolving rapidly.

I’m going to disagree with what Richard stated about Curran taking a decision and agree with Brian on Jorgensen, but I do not believe this fight makes it past the opening round as “Young Guns” scores a knockout.

FW: Hatsu Hioki (24-4-2) vs. George Roop (12-7-1)

Wilcoxon: Hioki is currently ranked as the No. 2 featherweight in the world. He has defeated the best in the world during his run in Japan, including Marlon Sandro, Mark Hominick and Rumina Sato. He possesses solid striking and smooth submissions.

Hatsu Hioki (Taro Irei/Sherdog)

Roop is still be remembered for his run on The Ultimate Fighter, and that is unfortunate. Roop has improved so much since then. He is extremely tall for the weight class and his length causes difficulty for his opponents. He was the first fighter to finish the “Korean Zombie” Chan Sung Jung and also recently finished former top contender Josh Grispi.

Who you pick in this fight really comes down to if you believe the hype following Hioki or if you think he will fall into the line of fighters that includes names like Takanori Gomi, Norifumi “Kid” Yamamoto and Michihiro Omigawa, all of whom flourished in Japan and then struggled in the UFC. I think and hope Hioki is the real deal. MMA is much more exciting when top-ranked guys get to fight each other. I am going to take Hioki by a close decision, but Roop is a live dog in this fight.

McKenna: When the UFC signed Hioki, it was clear that he was brought in to be the guy to dethrone Jose Aldo. As Richard mentioned, the Japanese fighter is ranked among the best in the world and might be the highest ranked fighter in the world to never step foot inside the Octagon. However, Richard also beat me to what I was going to say about highly-touted Asian fighters coming to fight for the UFC and how they have not fared well recently.

His counterpart in this fight, Roop, did well in his time before the UFC, but struggled during his first stint in the promotion. One thing was clear and that was his home was not at lightweight, but rather in the lower ranks at featherweight. Even though he has not excelled at 145 pounds, he has gone 2-1-1 in his last four fights, highlighted with the aforementioned finish of the “Korean Zombie,” which is better than his 1-2 stint at lightweight with the UFC.

Ultimately though, I don’t think that the TUF veteran has the ability to take down the “Iron Broom” in this fight. Not to say that the UFC put Roop against Hioki as an easy opponent, but they certainly could have been able to find stiffer competition. Because of this, Hioki starts his UFC career off with a bang by submitting Roop in the first.

George Roop (Rob Tatum/The MMA Corner)

Adams: I’ll be honest and say that I had to do some research on Hioki and from what I read, it appears that this guy is for real.

As my fellow panelists mentioned, whenever a Japanese fighter signs with the UFC, they tend to struggle, with the exception of Yushin Okami. However, I think “Iron Broom” will make a statement to the UFC in his debut. The 28-year-old has only lost once in three years, so expect a good showing from Hioki.

Roop is a guy I’m just not so sure of. He has had his high points, destroying Jung and upsetting Grispi, but has also had his lows, not staying consistent. The fighters he has lost to have been very talented, but it’s just hard to establish which tier the Team Tompkins fighter belongs in. After this fight, we will determine that.

I’m going to agree with both Brian and Richard and take the Japanese superstar. I just think his skill-set will be too much for Roop and Hioki will earn a clear-cut decision win.

HW: Mirko “Cro Cop” Filipovic (27-9-2) vs. Roy Nelson (15-6)

Adams: It appeared after two straight losses for Cro Cop that his MMA career would be over, but the 37-year-old has decided to step back in the Octagon for at least one more time.

The losses Cro Cop suffered weren’t against mid-level competition, however. He fell to a devastating knee from Frank Mir at UFC 119 and then took on rising heavyweight Brendan Schaub, losing in the third round by knockout. In my eyes, it’s as if Cro Cop’s game is going downhill and he will have a tough task at hand against “Big Country.”

Nelson is in a slide himself, losing in his last two outings to Junior dos Santos and in a fight he was the favorite in against Frank Mir at UFC 130. The TUF 10 winner desperately needs a win in this fight and more importantly, needs to show that he has the endurance to fight high-level guys in the UFC.

My heart is telling me that Cro Cop is going to win this fight in spectacular fashion, but my mind is telling me to go with Nelson. In the end, I’m going to go with Nelson by third-round submission after he is able to take the fight to the ground.

Wilcoxon: Cro Cop is one of my all-time favorite fighters to watch. His devastating kicks and strikes were a thing of beauty in his heyday. Bu those days were a long time ago. Cro Cop is just 2-3 in his last five fights and he was losing the fight with Pat Barry as well before pulling it out. His once iron chin is now porous as all of those losses have come via TKO. Cro Cop still has a good takedown defense and submission defense, but his bread and butter has always been his striking game.

As Corey mentioned, Nelson has struggled as of late. He is just 2-4 in his last six fights. However, he also ran through the TUF house during that span and those fights don’t show up on his record. Nelson is known for his large stomach, but despite his appearance, he is a well-rounded fighter. Nelson is a BJJ black belt and has KO power.

Mirko Cro Cop (r) (Rob Tatum/The MMA Corner)

I am a Cro Cop fan and always will be, but it has gotten to the point where I am legitimately worried about his health every time he fights. I see Nelson in this fight by pretty much any means he wants; either a devastating KO, a slick submission or riding out a decision.

McKenna: Rarely are match-ups between fighters who are both on two-fight losing streaks on the pay-per-view portion of a UFC card, but when you factor in that one of them is a recent TUF champion and the other is a legend of the sport, it is understandable as to why you will indeed need to pay to see this fight.

But let’s be real when we talk about this fight. The health concern for Cro Cop that Richard speaks of is a real problem. Dana White himself wanted him to retire after his last loss, but didn’t force him to because he still had a contract with the promotion. There was a time and a place where he was one of the most feared strikers on the globe, but that was many moons ago.

On the other hand, we have Nelson, a fighter who brags about being a “fat guy” but despite his tough chin and jiu-jitsu skills, he hasn’t gotten it done since taking down Stefan Struve in March of last year.

To echo what Richard said, Nelson has the ability to end this fight by multiple means. The only way I cannot see “Big Country” ending this fight is by head kick, which is Filipovic’s specialty. Still, he won’t need it, and Cro Cop won’t land it, as Nelson hands the Croatian his third straight loss.

HW: Cheick Kongo (16-6-2) vs. Matt Mitrione (5-0)

McKenna: The last time we saw Kongo in the Octagon, we all had to pinch ourselves to make sure that we were not dreaming. He took on Pat Barry and was all but finished early in that fight, but somehow he hung on, survived and landed a bomb of his own which was the start of the end of the fight. Critics of that fight will say that it should have been over early and that Barry should have been awarded the victory, but one way or another Kongo hung on and removed all doubt. That victory was huge for Kongo, who had previously been a stepping-stone type of fighter. Had he lost, it would have been two straight winless fights and it would have made him 1-3-1 since UFC 99. With a victory on Saturday, Kongo could finally breakout and put himself towards title contention.

A product of the UFC’s reality show, Matt Mitrione will enter the cage at UFC 137 with an undefeated record. Unable to find his groove while playing professional football with the New York Giants and Minnesota Vikings, the Illinois native decided to make the switch to MMA and has not looked back. He did reasonably well on the reality show and proved that he could indeed fight, even though he lost in the second round. From there, he went on to win in the Finale and has not looked back. The biggest knock at this point in his career though is that he hasn’t defeated anyone tough. His five fights have come against Marcus Jones, Kimbo Slice, Joey Beltran, Tim Hague and Christian Morecraft.

This is a clash of two fighters trying to legitimize their careers. This fight will be dominated by striking, and could get pretty sloppy if it makes its way to the ground. I have to go with Kongo in this fight, mostly because of his experience, but also on his ability. This is not a knock against Mitrione though, as it will be a good loss to have on his young MMA career, which will motivate and educate him further in the sport.

Wilcoxon: Mitrione is a relative newcomer to the UFC. Only five fights into his professional career, he has shown steady improvement. His striking, scrambling and wrestling all look better each time out. While his career is young, Mitrione isn’t. He is already 32. The UFC has slowly built his career. Each fight has been a small step up and Kongo continues that pattern.

Kongo entered the UFC as a kickboxer. He had polished striking, but in recent years Kongo has been practicing his wrestling. His takedowns have drastically improved. But while becoming better rounded, Kongo has fallen into the role of gatekeeper.

I think this fight will be a fun one for the fans. Both fighters strengths are the same. With both fighters sharing similar strengths, the winner of this fight will come down to athleticism, power, heart and determination. I think heart and determination have been the key to most of Mitrione’s wins. I look for Mitrione to take this with either a late TKO or a decision.

Adams: This is a solid co-main event in my opinion, as two heavy-hitters will throw leather until one man falls.

I really like what Brian said about the opponents Mitrione has faced. He is correct that Mitrione hasn’t fought a top-10 UFC heavyweight and this will be a challenge as he steps into the Octagon against Kongo.

I witnessed the Barry-Kongo fight and it was absolutely crazy! Many may say that Kongo got lucky in that fight, but whenever someone can come back to win a fight after a shot from Barry, I have the utmost respect for them. Another advantage Kongo possesses besides his power is the fighters he has faced: Mirko Cro Cop, Cain Velasquez and Frank Mir, to name a few. Kongo has faced the best heavyweights in the world.

After adding up all the factors in this bout, all signs point to “The Darkness,” who will earn a decision over Mitrione.

WW: B.J. Penn (16-7-2) vs. Nick Diaz (25-7)

Wilcoxon: Even before GSP and Carlos Condit were moved off this card, this was the main event in my eyes. This was the closest fight on the card and the toughest fight to predict.

Penn is the former welterweight and multiple-time lightweight champion. His BJJ skills were off the charts and led to his nickname of “Prodigy.” But despite those amazing ground skills, it has been Penn’s KO power and striking skills he has displayed most often in MMA. Penn re-invented himself again in his last bout where he displayed surprising wrestling skills early in his fight with former collegiate wrestler Jon Fitch.

Diaz was the last Strikeforce welterweight champion. He is entering into his second run with the UFC. In his first run, he went 6-4. Since leaving the promotion, he has gone 11-1 with one well publicized no-contest. Diaz is a BJJ black belt who has developed an awkward but effective striking style.

I think this entire fight depends on how Penn chooses to approach it. In Penn’s last fight, he showed excellent takedowns. Diaz has always struggled against wrestlers. If Penn uses his takedowns, I don’t believe Diaz can submit Penn or vice versa, but Penn could coast to a decision victory. However, if Penn decides to exchange with Diaz, he is playing with fire. Diaz has a huge reach advantage and throws punches in bunches that will score points and could score a TKO on Penn at some point.

I would like to say Penn will create the smart game plan and will ride his new-found wrestling to a decision victory, but game plans have never been Penn’s strength. In a coin flip, I will take Diaz via decision, but Penn has the skill to surprise me and just as easily could win by decision.

Adams: When I first heard that Georges St-Pierre was forced out of the event due to injury, I was shocked and upset all at the same time. But I had to remember the fight on the card that I really want to see go down: Penn vs. Diaz. Even though GSP won’t be defending his belt at UFC 137, this PPV will still be worth the buy to watch the new main event.

The former UFC lightweight champion has been out of action for quite a while, due to the fact him and Jon Fitch were expected to have a rematch of their draw at UFC 127, but that never happened. “The Prodigy’s” career is starting to go more downwards than up, but a win over Diaz would give his confidence a major boost to continue competing in top form.

Diaz makes his move over from Strikeforce and instead of not taking on GSP for the belt due to several reasons, he has now been put up against Penn. The key for Diaz is to make this an ugly, knock-down, drag-out fight. That’s how the Diaz brothers from Stockton, Calif., fight and do so effectively.

Even though Diaz does have a style of fighting that is hard to counteract, my hunch is that the veteran Penn will not allow him to land the numerous, wild punches. I think Penn will be the safer fighter and pull out a narrow decision victory.

McKenna: Like my fellow panelists, I too think that this fight is of the caliber to be a strong main event fight, but personally I would have preferred to see St-Pierre vs. Condit as the main event, but this will have to do.

Penn enters this fight as the man with the burden and weight on his shoulders. Not a lot of people would have wanted to take on Diaz in this fight because even though it is not really being advertised as it, this fight is to determine whether or not Strikeforce fighters are worth a damn. But the Hawaiian isn’t the only one who has pressure on him, because Diaz also has to keep in mind that he is representing his former brand, too.

Say what you want about how the Stockton native blew his shot at St-Pierre because he didn’t show up to press conferences, and how he frequently is late and blows off other appearances, but Diaz can fight, and fight well. He is currently riding a 10-fight winning streak including three straight title defenses, but now he has to take on a different beast while returning to fight for the UFC. That will be the biggest factor in this fight, and that is why the former Strikeforce champion will lose. Look at who he has taken on in his last five fights: A UFC castaway, Cris Cyborg’s husband, a boxer, a Japanese star nearly ten years past his prime and a Dream champion who has proven to be mediocre at best. Meanwhile, Penn was fighting Jon Fitch, Matt Hughes, Frankie Edgar twice and Diego Sanchez. Iron forges iron, and that is why Penn will be sharper and achieve the decision victory over Diaz.

Top Photo: Nick Diaz (Sherdog)