NEWARK, N.J. — Georges St. Pierre methodically defeated challenger Dan Hardy in a unanimous five-round decision in the main event of UFC 111 and retained his welterweight championship last night.

St. Pierre, from Montreal, won his seventh straight title defense and improved to 20-2 in his UFC career.

"I made a lot of mistakes that I'm not happy with," St. Pierre said. "I wanted to fight him on the ground where I am the strongest and I know he's the weakest. But he was a lot tougher than I thought he was.

"I wanted to finish the fight in an impressive way, but I didn't. I will work with my trainers and come back stronger and better. I can't make mistakes like that."

Hardy, from Nottingham, England, dropped to 23-7 overall. It was Hardy's first title fight.

"I might lack the technical skills and I might lack the strength," Hardy said. "But the one thing I have is that I'm never going to quit. I don't give up. I never give up. I don't know the meaning of tapping out."

St. Pierre, fighting for the first time in eight months after undergoing abdominal surgery, took control of the bout with a double-leg takedown within the first 10 seconds.

Earlier, undefeated Shane Carwin knocked out former champion Frank Mir at 3:28 of the first round to win the UFC interim heavyweight title.

Carwin, a former college football player and wrestler at Western State in Colorado, controlled the bout from the beginning and eventually got to Mir with two powerful left-handed uppercuts, knocking him to his knees.

Carwin (12-0) then pummeled Mir (13-5) with a series of 27 unanswered punches, forcing referee Dan Miragliotta to stop the fight.