LAS VEGAS — Randy Couture stopped Mark Coleman with a rear naked choke Saturday night to win a bout between two UFC hall-of-famers in their mid-40s.

The five-time champion took Coleman down early in the second round and quickly gained the mount position.

Coleman, who at 45 is a year younger than Couture, rolled and gave up his back to Couture, who then sunk in the submission attempt and forced the referee to stop the fight at 1:09 of the second round.

Couture is the oldest fighter to compete in the UFC and still has plans to regain the heavyweight championship he has held on three previous occasions.

In the earlier co-main event, Chael Sonnen beat Nate Marquardt by unanimous decision, earning a shot at the middleweight title.

All three judges had it 30-27 for Sonnen, who will face the winner of the Anderson Silva-Vitor Belfort bout in April.

Sonnen controlled Marquardt for much of the fight, taking him down multiple times and landing a number of solid blows.

Marquardt opened a large gash above Sonnen's eyebrow and nearly locked him in guillotine choke late in the final round but couldn't neutralize Sonnen's Olympic-level wrestling skills.

In earlier fights, former welterweight champ Matt Serra TKO'd Frank Trigg in the first round, flooring him with an overhand right and forcing the ref to stop the fight with a flurry of punches.

Paulo Thiago submitted Mike Swick with a D'Arse choke in the second round and middleweight contender Demian Maia won a unanimous decision over Dan Miller.

Mac Danzig, Melvin Guillard, Rob Emerson, Phil Davis, Chris Tuchscherer and Joey Beltran also earned victories on the card.