LAS VEGAS - Brock Lesnar is officially the Ultimate Fighting Championship's next big thing.

The former Bismarck State College wrestling champion scored a knockout of UFC heavyweight champion Randy Couture at 3:07 of the second round on Saturday in their title fight at UFC 91.

Lesnar, who improved his MMA record to 3-1, scored the win despite a huge disadvantage in experience to Couture, a five-time UFC champion.

"I just believe in hard work, and that it pays off, honest to God," Lesnar told Joe Rogan on the pay-per-view telecast "I may come across as a cocky SOB, but I'm just confident. … I've got the utmost respect for Randy Couture."

The first round was relatively even, with Lesnar having a slight edge. Couture landed a solid right at 1:15, but Lesnar scored a takedown at two minutes. Couture nearly escaped, but Lesnar muscled him back to the mat. Lesnar landed a punch at 1:30, but Couture was able to get back to his feet.

In the second round Lesnar landed a right elbow just 15 seconds in, but Couture forced him into the cage and they clinched. About 1:20 in, Couture opened a cut by Lesnar's right eye.

But Lesnar landed a high knee with 2:13 to go. Then Lesnar, who has shown lethal punching power in all his fights, knocked down Couture with a right hand that grazed his temple. From there, Lesnar pounced on Couture and rocked him with hammerfists and elbows until the fight was stopped.

"It's hard to get out of the way of those," Couture said of the knockdown punch. "… He's just a big guy, and he caught me with a big shot."

Lesnar won the NJCAA heavyweight wrestling championship in 1998 while wrestling at BSC. He went on to win an NCAA title for the University of Minnesota in 2000.

The 31-year-old Lesnar had only three MMA fights before his title shot. He defeated Min-Soo Kim, an Olympic silver medalist in judo, in the first round in his debut for another organization. In his first UFC bout, Lesnar was pounding former heavyweight champ Frank Mir but got caught in a knee bar and was submitted. Lesnar rebounded with a lopsided decision over MMA veteran Heath Herring in August.

Couture (16-9) is a five-time UFC champion, three times at heavyweight and twice at light heavyweight, and a member of UFC's Hall of Fame. But the 45-year-old had not fought in more than a year because he was embroiled in a contract dispute with UFC.

Couture was an All-American wrestler at Oklahoma State University and a four-time national Greco-Roman wrestling champion.

The winner of Saturday's bout is expected to face the winner of the Dec. 27 match between Mir and Antonio Rodrigo Nogueira, who won the interim heavyweight championship in Couture's absence.