LAS VEGAS - Younger, bigger, stronger, faster. Brock Lesnar ran the table at UFC 91.

The six-foot-three, 275-pounder left 45-year-old Randy (The Natural) Couture crumpled in his wake Saturday night from a near sellout of 14,272 at the MGM Grand Garden Arena. The UFC heavyweight champion gave it his all before giving up his title via second-round TKO to Lesnar (3-1).

Lesnar, 31, wins the heavyweight crown in just his fourth mixed martial arts fight. Couture did the same thing 11 years ago when he beat Maurice Smith but mixed martial arts was in its infancy then.

Most fighters are nowhere near the UFC after just four fights, let alone bidding for the title. But the hulking Lesnar is different, an imposing physical specimen with a unique background that includes an NCAA wrestling title and time in the WWE.

Lesnar figures he has only gone a "quarter-mile" down the MMA road. More opponents will be hurt along the way while he learns the sport, adding submissions, kicks and other weapons to his arsenal.

"Brock is an amazing athlete and such a big guy," UFC president Dana White said. "So far he's gotten by on athleticism and size. As he continues to grow as a fighter and gets more technical, God knows what this guy's going to do."

The fight ended when Lesnar caught Couture (16-9) with a right hand behind the ear. A stunned Couture went down -- "Next thing I know I was on the ground, eating leather" -- and Lesnar pounced, delivering more than two dozen hammer-fists and punches until referee Mario Yamasaki finally stepped in three minutes seven seconds into the round.

Yamasaki would have done Couture a favour by stopping it earlier.

"You could tell Mario was trying to give him time, but there's that fine line between giving someone time and taking too many punches," White said. "And when the fight was over and Randy wasn't getting up quick, then I started to think `Oh shit, maybe he should have stopped that sooner."'

Couture seemed fine after the fight, other than some facial lumps and abrasions. But the prolonged finale did little to impress one German reporter, part of a group the UFC was entertaining over the weekend in advance of a possible show in Germany.

"Of course such a fight raises particular questions in our country," said the German reporter, who questioned the repeated punching at the end.

"The rules of engagement are that you punch a guy in the head," answered Couture. "Until the referee steps in and stops the fight, why would he stop punching me in the head?"

MMA was sanctioned by athletic commissions across the U.S., he reminded the reporter

Couture, at 6-2 and 220 pounds, was giving up 14 years, at least 50 pounds and six inches in reach to Lesnar. He also hadn't fought for 15 months.

The fight may have signalled the latest changing of the MMA guard.

Former light-heavyweight champion Chuck (The Iceman) Liddell, Couture's onetime nemesis, is 38 years old and has lost three of his last four fights. Couture was beaten coming out of his second retirement.

Today's champions are younger and, unlike Couture and Liddell, essentially learned mixed martial arts as a whole rather than coming out of one discipline and adding to their toolbox.

Montreal's Georges St. Pierre (welterweight champion) is 27, B.J. Penn (lightweight) 29 and Anderson Silva (middleweight) 33.

Lesnar, a former NCAA wrestling champion and WWE star who was the 7-5 favourite with the bookies, came out first to the booming sound of Metallica's "Enter Sandman" -- and a chorus of boos. The cheers started before Couture, a former four-time alternate on the U.S. Olympic Greco-Roman team, made his entrance to Aerosmith's "Back in the Saddle" -- with his shiny championship belt held up high by one of his trailing crew.

Couture escaped in the first round when Lesnar took him down. And he scored some blows coming out of the clinch. But Lesnar shook him every time he connected.

"I knew in my heart, in my mind, I could take him down. And after getting in a few exchanges with him, I felt like I was connecting with him," said Lesnar. "He connected with me but quite frankly I just felt like I was hitting harder and I was going to connect before he did."

All three judges awarded the round to Lesnar.

The big man was cut by the right eye in the second as Couture caught him with a good punch as they separated from a clinch. Lesnar pawed at his eye, as if wondering what had happened.

"Right away, it made me a little nervous," he said of the cut. "But then it pissed me off. I wanted to get first blood on Randy. Any time you fight, you want to get first blood. Something in my head just went `All right, we've got to pick this up.' And that's what I did."

It ended suddenly when Couture was tagged with the right and could not escape the barrage of blows.

Couture, the master strategist, was unable to solve this giant problem. It was like tackling a souped-up mini-van.

Couture did leave a mark, with Lesnar needing four or five stitches to close the cut. As to his future, Couture said he wanted to take some time to "let the dust kind of settle.

"We'll figure it out," he added. "I'm sure it will come to me."

There was almost an element of good versus evil in the buildup to the main event with fans wildly cheering any glimpse of Couture while booing Lesnar. Couture was returning from his second retirement, this time due to a contract dispute.

"Randy Couture is a living legend. He's a guy that everyone loves . . . It's tough to see your heroes get beat," White said. "Over the next however long Brock commands the heavyweight division, I'm sure people will start to take to him. If you don't like him, eventually you'll have to respect him."

According to the Nevada State Athletic Commission, Lesnar made US$450,000 -- including a $200,000 win bonus. Couture was guaranteed $250,000, missing out on a matching win bonus.

Those figures do not tell the whole tale since they do not take into account other contract bonuses not made public by the UFC. Couture is also likely to collect a cut of the lucrative pay-per-view take from the night -- the UFC predicted a record 1.2 million buys for a take of more than C$50 million, not counting the arena gate of US$4.8 million.

Lesnar will next meet the winner of the December fight between Antonio Rodrigo Nogueira and Frank Mir. His preferred opponent is Mir, a former heavyweight champion who submitted him in his UFC debut in February.

After a thin period, the heavyweight division is showing signs of life with Lesnar and newcomers Cain Velasquez and Shane Carwin and the resurgence of Gabriel Gonzaga.

"I think it's getting stronger and stronger. Brock is a great indication of where the heavyweight division is going," Couture said. "We're getting these guys that aren't just big guys. They're very good athletes."

Couture and Lesnar were both gracious after the fight, although Couture sounded a warning to Lesnar that others would be gunning for him as he continued his mixed martial arts education.

"It's fun (expanding the MMA arsenal) but you've got to step out there in the cage and prove it every time too. And sometimes carrying that belt around makes you a target."

Lesnar admitted to nerves before the bout and got emotional at the post-fight news conference when asked what winning the UFC championship meant to him.

"My first NCAA title meant a lot to me but this, I never expected this in my wildest dream. I don't know even what to say."

In the co-main event, lightweight Kenny Florian choked out Joe (Daddy) Stevenson in the first round.

Canadian lightweight Mark Bocek (6-2) scored an impressive third-round submission win over Alvin (Kid) Robinson.