The first two rounds were close, but Condit took over in the third and fourth. Diaz managed to secure back control in the fifth, but Condit escaped the rear-naked choke attempt. The judges unanimously awarded the bout to Condit with scores of 48-47, 49-46 and 49-46.
With the victory, Condit is now the interim UFC welterweight champion and will face Georges St. Pierre to unify the two titles.
“It's pretty surreal,” Condit said. “I couldn't have done it without my coaches and my teammates. They prepared me and I did what they told me to.
“Hats off to Nick Diaz. I have nothing but admiration for the way he fights.
“It is an honour (to fight St. Pierre). Georges a guy that I looked up to since I was young.”
They don't breed them any tougher than Roy Nelson.
The Ultimate Fighter season 10 winner took a barrage of vicious knees and punches from Fabricio Werdum in the co-main event of UFC 143 in Las Vegas Saturday.
Werdum bloodied Nelson early and hurt him often throughout the 15-minute war. Werdum landed numerous shots that would have knocked out most heavyweights, but Nelson just kept moving forward.
Though he showed a ton of heart, Nelson was simply out-worked for all the rounds, losing a unanimous decision.
"I know Roy Nelson a big, tough guy," Werdum said to interviewer Joe Rogan. "I put my knees on him because I'm always training knees and Muay Thai.
"I'm confident in my guard. He was punching me, but he didn't hit me. He punches hard."
Josh Koscheck won a questionable split decision over Mike Pierce.
Koscheck looked hesitant, allowing Pierce to land small combinations and dictate the pace. Though Koscheck got the better of the wrestling exchanges, he never really mounted any significant offence.
However, two judges scored it 29-28 for Koscheck, eliciting a chorus of boos from the fans in attendance.
"You guys boo me all the time," Koscheck said. "I'm the most hated guy in MMA, but guess what - deal with it.
"Mike Pierce is a tough guy. I knew that coming into this fight."
Renan Barao took another step towards a bantamweight title shot, winning an entertaining stand-up battle against Scott Jorgensen.
"I have worked very hard and this feels great," Barao said. "I was ready for this moment. The title is my goal. I train every day and I'm ready for it. "
It was clear Barao's sharp striking and takedown defence frustrated Jorgensen, who was mostly able to only land jabs throughout the first two rounds. Even when he did connect, Barao made him pay every time.
Jorgensen managed to find some success with his combinations in the third, but was still unable to out-strike Barao. After 15 minutes of fighting, the judges unanimously scored the bout 30-27 for Barao.
Ed Herman weathered the early storm, submitting Clifford Starks with a rear-naked choke in the second round.
Herman had trouble with Starks' striking, eating numerous straight rights. But after tripping Starks to the mat, he transitioned to full mount. Starks attempted to roll over, exposing his back and allowing Herman to secure the choke.
"He's was landing some good rights on me," Herman said. "Luckily I've got a good chin because he hit me hard.
"I like that sweep. It's one of my favourites. I knew with him being a wrestler that he would give up his back."
Dustin Poirier pulled off one of the best submissions of the year, finishing Max Holloway with a mounted triangle armbar in the final preliminary bout.
"I never underestimated Max; I was in his shoes before," Poirier said. "He's a tough fighter and good kickboxer. He was quicker than I expected though and hit me with a few shots. I wanted to come out strong and mix it up with some kicks. I came here to get a win, and I got the finish. I'm one step closer to being a champion."
After a failed armbar attempt, Poirier transitioned to a triangle choke. From there he rolled Holloway onto his back to secure the mount. Poirier then torqued the arm for the stunning victory.
Edwin Figueroa won a controversial split decision over Alex (Bruce Leroy) Caceres.
"I felt like it was a hard earned paycheck," Figueroa said. "He was a good fighter. I had to dig deep for this one. He came out and landed a few shots early. It was a tough fight but I came out the winner."
Much of the bout saw Caceres dominate Figueroa, but referee Herb Dean surprisingly deducted two points for a pair of unintentional groin shots. On top the questionable reffing, fans and critics will likely debate the first round. Caceres controlled most of the action, but was dropped with a hard high kick.
After three rounds, two judges scored the bout 28-27 for Figueroa.
"I don't know what happened. I thought I had that one," Caceres said. "I guess they took points away from the low blow I delivered. I didn't take that much damage. I'm very disappointed."
Earlier in the night, Matt Brown handed Chris Cope his second consecutive knockout loss in a battle of TUF veterans. TUF alum Matt Riddle won a close split decision over late replacement Henry Martinez in an exciting striking war. Brazilian jiu jitsu black belt Rafael Natal survived a late scare before turning the tables to secure a one-sided unanimous decision over Dutch kickboxer Michael Kuiper. Undefeated karate sensation Stephen Thompson delivered a knockout-of-the-year candidate, flattening Dan Stittgen with a slapping high kick in his UFC debut.
UFC 143 RESULTS
Carlos Condit def. Nick Diaz via unanimous decision (48-47, 49-46, 49-46)
Fabricio Werdum def. Roy Nelson via unanimous decision (30-27, 30-27, 30-27)
Josh Koscheck def. Mike Pierce via decision (28-29, 29-28, 29-28)
Renan Barao def. Scott Jorgensen via unanimous decision (30-27, 30-27, 30-27)
Ed Herman def. Clifford Starks via second-round submission (rear-naked choke)