The Ultimate Fighting Championship has a new heavyweight champion.

"It sounds really good," Brock Lesnar said after being introduced as the new heavyweight champion. "I can't believe it."

Newcomer Lesnar defeated the reigning champ, Randy "The Natural" Couture, in the Ultimate Fighting Championship 91 in Las Vegas on Saturday.

Lesnar, who entered the fight with a 2-1 record, as opposed to the veteran Couture's 16-8 mark, was declared the winner by TKO at 3:07 in Round 2 of the five-round heavyweight title bout.

Couture, who was returning to the octagon after a more than a year layoff during a contract dispute with the UFC, entered the cage to Aerosmith's "Back in the Saddle." For a while, the 45-year-old champ looked like he was back in championship form.

Lesnar got a takedown in Round 1, but Couture was able to fight him off and got back to his feet, showing the former NCAA wrestling champion that he'd need to work for a victory.

Early in Round 2, Lesnar landed an elbow on Couture before the Las Vegas resident landed a shot on Lesnar that caused a stream of blood to run down the former professional wrestler's face.

But then Lesnar fought back. The 31-year-old South Dakota native landed a right knee to Couture's chin. He then landed a right hand behind the ear and followed with a flurry of punches. Referee Mario Yamasaki stepped in and called the fight at 3:07 in the second, awarding Lesnar the victory.