Diaz dominated the pre-fight trash talk by a large margin, but St-Pierre dominated the fight in an equally wide manner at UFC 158.
It was a typical St-Pierre fight: He repeatedly took Diaz down, though he rarely did much with those opportunities. He landed some hard shots in the first, clearly his best round. But as the fight progressed, he simply controlled Diaz, who was unable to land many significant strikes.
All three judges had it 50-45 for St-Pierre, the same as Yahoo! Sports saw it.
"I knew he was good in boxing range and I wanted to stay out of his boxing range," St-Pierre said. "I used my karate."
When the match ended, St-Pierre tentatively offered his hand to Diaz, who grabbed it and shook it. Diaz then patted St-Pierre on the face. St-Pierre later told the crowd that Diaz is a good guy.
Diaz offered precious little offense. He couldn't land much in the striking game and spent much of the fight on his back. He showed his toughness by taking a lot of punishment.
"I want to thank Georges St-Pierre for giving me the credit I think I deserve," Diaz said.
St-Pierre was more aggressive early, but as the fight progressed, he took his foot off the gas and seemed content to hold Diaz down and avoid danger.
Diaz, a black belt who has elite jiu-jitsu, never seriously threatened a submission.
After the fight, he suggested that he's considering retirement.
"I apologize to my hometown, Stockton," Diaz said.
St-Pierre will likely next defend his belt against Johny Hendricks. Hendricks broke his left hand sometime in the middle of his welterweight fight with Carlos Condit, but that didn't stop him from winning one of the year's best fights.
Hendricks earned a welterweight title shot with an electric unanimous decision victory over Condit. All three judges had it 29-28 for Hendricks. Yahoo! Sports saw it 29-28 for Condit.
Hendricks was looking to land his trademark big left hand, and he caught Condit with it several times.
Condit, who has one of the best chins in the game, not only took the shots, but he would fire back with his own. He rocked Hendricks several times with punches and knees.
At the end of the fight, UFC president Dana White and CEO Lorenzo Fertitta stood up and applauded their effort along with the rest of the massive crowd.
"Much respect to Carlos," Hendricks said. "I am banged up. I hit him very hard, big shots, but he kept coming and coming. He's an awesome fighter."
When it was over, Hendricks pleaded for the title shot he thought he was going to get after he knocked out Martin Kampmann in November.
"I want GSP next if he wins this fight," Hendricks said after he beat Condit. " ... I have more than earned it. What did GSP do to earn his two title shots? What did Diaz do? Lose a fight to the guy I just beat. GSP didn't go through the contenders like I did. I have beaten the same guys way more impressively than he has. Condit didn't knock me down but he had GSP out.
"I'm banged up but I will be ready whenever he is. He can fight me here in Montreal, or any arena anywhere in the world. That, or I grab Dana White, I hire the Octagon myself, I hire a ref and I show up at his house, ring the door bell and we fight right there on his porch. He's got nowhere to hide now."
In the card's other key welterweight bout, Jake Ellenberger showed exactly why he has the third-most knockdowns in UFC welterweight history against Nate Marquardt.
Ellenberger hadn't been able to do much for the first two-plus minutes of their bout. But then, he landed a left hook and later a crushing right cross that sent Marquardt down to the canvas.
Ellenberger landed a few shots from the top before referee Phillippe Chartier jumped in to stop it at 3:00 of the first.
It was a huge win in the division for Ellenberger and will keep him near the top of the rankings and in the mix for a title shot.
"He kicked me hard to the leg and one to the body and I thought, 'OK, we are going to end this fast,' " Ellenberger said. "I saw he squared up whenever he kicked so I threw hard every time he did that. This is no doubt the biggest KO of my life, and it puts me right there for a title fight or No. 1 contender fight.
"I want to say something: After the Kampmann fight there were people saying I was gun shy and not the same fighter. I showed tonight that's total b.s. I can knock out anyone in the division and I go for the KO every chance I get. The setback in the Kampmann fight only made me stronger. I'm very happy right now."