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 tonight.

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.

Although St. Pierre had never wrestled in high school or college, he utilized his superior wrestling skills throughout the fight and was never seriously challenged or hurt by Hardy.

Hardy, sporting a red Mohawk haircut, remained on his back for most of the first round and was almost driven to submission with a ferocious arm bar, but Hardy escaped and got to his feet in the closing seconds of the period.

In the second round, St. Pierre used a single-leg to get Hardy to his back again, holding control for most of the round.

Hardy did gain a reversal and put St. Pierre to his back, but managed nothing from it, as St. Pierre quickly escaped.

In the fourth round, St. Pierre almost got Hardy to submit with another arm bar, but Hardy managed to work his way out of the hold, sending the bout to the fifth and final round.

St. Pierre maintained control, totally dominating his opponent. Although Hardy never threatened, he did not submit.

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 then pummeled Mir with a series of 27 unanswered punches, forcing referee Dan Miragliotta to stop the fight.

Carwin and Mir were the undercard to the main event between Georges St. Pierre and Dan Hardy.

Carwin improved to 12-0 as a professional and has now earned the right to take on champ Brock Lesnar sometime this summer.

Lesnar is recovering from emergency surgery after a hole was found in his intestines due to a bacterial infection. Carwin had two bouts with Lesnar canceled due to Lesnar's illness. Lesnar was standing outside the cage when the fighters entered the octagon Saturday night.

Mir's record dropped to 13-5.