The ante has been upped significantly with the reigning champion at welterweight facing current champion at lightweight during the prime of both men's careers. This alone makes it a must-see event, but there's another reason that compels audiences to witness this moment in history: Penn, 13-4-1, and St. Pierre, 17-2, represent the most sophisticated evolution of the modern MMA fighter, with both men being incredibly well-rounded in all areas of the sport. They are among the upper echelons of the pound-for-pound list and are eager to face each other in a bid to cement their legacies.
As Saturday approaches, St. Pierre holds his cards close to his chest, unwilling to play into a war of words.
"I don't focus on what he's saying about me, I just focus on what I'm going to do to him," St. Pierre told ESPN.com. "He can say whatever he wants. A lot of people can talk -- it's easy to talk, but it's harder to walk the walk."
For his part, Penn makes it clear that he's being misconstrued as the antagonist in a bid to market the fight as good guy versus bad guy.
"I think GSP is always careful and watches what he says so he doesn't come off like the bad guy," Penn said. "I don't think you get exactly what you see with GSP."
While Penn is heard making statements about wanting to kill GSP, St. Pierre comes across as the polar opposite, even going as far as saying he likes Penn.
No one is more familiar with how each man operates in the Octagon than welterweight Matt Hughes (42-7), who went 1-2 against St. Pierre and 1-1 with Penn. Drawing on his own experiences, Hughes shed some insight into what might unfold on Jan. 31.
"It's a very interesting fight," Hughes said. "The winner is going to come down to who has trained the hardest and who is on their game that day.
"The stand-up edge will go to B.J. Penn but I think the wrestling edge will go to GSP. Real close fight, but I got to say B.J. is going to have a little bit of an advantage if he can last all five rounds."
Although Penn looked born-again in retaining the lightweight title via third round TKO against Sean Sherk (33-3-1) in May, Hughes is pessimistic over whether Penn has answered all the questions about his conditioning.
"Sherk really didn't put any pressure on him and B.J. loves to stand up so it was very comfortable," Hughes said.
Penn takes aim straight at what he thinks is GSP's biggest weakness -- his heart.
"[St. Pierre] is the type of guy who, when he's in danger, he won't keep going," Penn said. "I believe he'll quit."
Penn's belief in his own invincibility has guided him through a career laced with unknown quantities. He submitted a 14-1 Takanori Gomi in 2003 and captured his first title in 2004 against Hughes at welterweight, outside his natural weight class of lightweight. In 2005, Penn lost a very close decision against current undefeated light heavyweight Lyoto Machida (13-0).
St. Pierre, though, has been just as dominant, smashing through a who's-who list of opponents. Still, he remains respectful of Penn, even admitting he has no hard feelings beyond what will take place in the Octagon on Saturday.
Above and beyond the contrasting backgrounds of St. Pierre and Penn -- working class versus island elite, cold Montreal versus tropical Hilo, humility versus arrogance -- GSP points to another fundamental difference between their styles.
"It seems to me like BJ Penn is fighting with his fear," St. Pierre said. "Fight from his fear and from his anger. I fight from my heart, fight from love."
B.J. has made a habit of instigating scheduled opponents on every occasion he's had the chance: questioning Jens Pulver's right to coach opposite him on Season 5 of "The Ultimate Fighter;" making a YouTube video of himself gorging on fast food before facing Joe Stevenson and raking Sherk over hot coals over his alleged use of performance enhancers.
But as much as Penn runs his mouth and tends to push the envelope, he claims his ferocious will to win was taken out of context during the taping of the UFC's "Primetime" special.
"They asked me 'What are you going to be thinking when you're standing on the other side of the ring from him right before the fight,'" Penn said. "I believe every fighter should be standing on the other side thinking, 'I'm going to kill this guy, I'm going to walk right through him,' because if you're not thinking that, then you might as well go play badminton or something else."
As Penn's fiery rage contrasts with GSP's coldly calculated presence, each promising to stick it out until the bitter end, they choose to converge on one point.
Neither man is willing to commit to the fatal error of looking past this fight by talking about who they will face next. That's not simply because the magnitude of this meeting requires total concentration, but also perhaps due to the realization that this is it -- this is the big one, the moment that could be remembered as the pinnacle of their careers.
"I think it could be the fight of the year," predicted Hughes.
There's a sense of anticipation and excitement that hasn't been matched in some time. Fight fans can only hope the event lives up to the expectations.
Brian J. D'Souza is a Canadian writer whose work has appeared on CBC.ca, men's magazine Sharp and FIGHT! magazine.