Sean Sherk claimed B.J. Penn wouldn't be the true champion until he defeated him in the Octagon.
Penn did just that Saturday night with a third-round stoppage of the former lightweight champion in the main event of UFC 84 at the MGM Grand.
Penn became champion by defeating Joe Stevenson earlier this year for the title Sherk vacated for testing positive for steroids. He retained the title when Sherk was unable to continue after a barrage of shots by Penn in the final 10 seconds of the third round.
Penn outboxed Sherk, mostly using the left jab to keep the shorter fighter at a distance.
But late in the third, a combination pushed Sherk back against the cage. Penn charged and knocked him to the mat with a knee to the head and then unloaded a barrage of shots right up to the bell.
The referee signaled an end to the round but then determined Sherk would be unable to continue.
Earlier, Tito Ortiz didn't mount any kind of offensive attack and lost a unanimous decision to Lyoto Machida.
With the win, Machida remained unbeaten and must be considered on the short list of title contenders in the light heavyweight division.
Machida won 30-27 on all three scorecards and owns five Ultimate Fighting Championship wins since he joined the organization in February 2007.
Through much of a mostly stagnant first round, Machida landed leg kicks and stuffed Ortiz's takedown attempts. Machida then powerfully took down the former champion in the round's final seconds.
Both fighters showed more activity in the third and final round. Machida dropped Ortiz with a solid knee to the midsection and followed him down to the mat in top position.
Ortiz, however, showed his only real offense of the fight when he nearly submitted Machida by locking in a triangle choke from the bottom.
"I was thinking, 'I'm going to die, but I'm not going to tap,' " Machida said.
It was the only chance Ortiz had to win the fight.
The fight was the last on Ortiz's UFC contract, but he didn't rule out the possibility of re-signing with the organization with which he has had so much discord.
"I haven't decided at all. I'm going to take two weeks off," he said. "I gave my life in this Octagon for the greatest fans in the world."
Wanderlei Silva's bout with Keith Jardine provided early fireworks. Silva ended a three-fight losing streak by knocking out Jardine in 36 seconds. Jardine was motionless for several minutes afterward but was alert in the locker room before going to the hospital.
On the undercard, Thiago Silva improved to 13-0 with a first-round knockout of Antonio Mendes.
Wilson Gouveia nearly stopped Goran Reljic in each of the first two rounds, but Reljic scrambled to his feet and dropped Gouveia with a huge left hand midway through the second. Reljic jumped on Gouveia and prompted a referee stoppage about 20 seconds later.
The night got off to a quick start when heavyweight Shane Carwin knocked out Christian Wellisch in 44 seconds.
Also, Dong Hyun Kim, Yoshiyuki Yoshida, Rameau Thierry Sokoudjou and Rousimar Palhares picked up stoppage wins, and Rich Clementi earned a decision over Terry Etim.