LAS VEGAS -- The underdog role seems to suit Forrest Griffin just fine.
Griffin stood up to all the doubters Saturday night and, more importantly, didn't back down to Ultimate Fighting Championships light heavyweight champion Quinton "Rampage" Jackson, winning a unanimous decision in the five-round main event at UFC 86 at the Mandalay Bay Events Center.
Griffin, a 5-2 underdog, overcame a first-round knockdown before answering back early in the second, hobbling Jackson with a snapping left leg kick to his right knee. That appeared to be a turning point, as Griffin then took Jackson down on his back and spent the next 4 1/2 minutes throttling him with elbows and fists.
"This is the best moment of my life," said Griffin, who made a name for himself while twice appearing on "The Ultimate Fighter" reality series. "I can't wait to do this again."
Jackson, who was making his second title defense since winning the belt from Chuck Liddell in May 2007, tried to weaken Griffin with a variety of combinations, but he seemed to have lost his leverage with the devastating kick to his back leg.
"He really hurt my leg," Jackson said afterward. "In the second round, I was on the ground the whole time. I was just trying to recover."
It was the second consecutive major upset for Griffin, a 29-year-old who honed his skills in Athens, Ga., and now lives in Las Vegas. Griffin was coming off a nine-month layoff after his third-round submission of Mauricio "Shogun" Rua, who was the last person to defeat Jackson before Saturday.
"I think that was pretty close," said Griffin, who won, 48-46, on two scorecards and 49-46 on the other. "We're going to have to do that again and that [stinks] for me."
A rematch should be greatly anticipated for mixed martial arts fans, who cheered loudly during the entrance of both fighters. Griffin entered the ring first and shadow boxed for several minutes as Jackson slowly made his way into the octagon, donning a thick metallic chain around his neck and a cold, blank stare.
Jackson, a 30-year-old Memphis, Tenn., native who now lives in Irvine, scored the first big blow, dropping Griffin (16-4) with a solid right uppercut with 1 minute 10 seconds remaining in the opening round. Jackson (28-7) pounced on Griffin, who managed to wriggle free, only to absorb more punches on the way up.
Jackson then found himself in serious trouble early in the second round, when Griffin nailed Jackson with a left kick to the right leg, a weapon that proved to be effective throughout the fight.
"Later in the round, it's something I wanted to do," Griffin said of the kicks. "I just went to it one too many times and he got a little elusive."
After the left kick, Griffin took Jackson down and grinded him with elbows, hammered him with his right fist and, at one point, attempted an arm bar.
The round appeared to take its toll on Jackson. He was able to land several combinations, but he appeared to have little snap to his punches. He pushed Griffin onto his back after a fourth-round combination and managed to open a cut over Griffin's right eye, but the challenger again battled back.
With both fighters appearing exhausted by the fifth round, Griffin was able to land the better combinations, though none staggered Jackson as much as the second-round leg kick.
"He just whupped my butt," Jackson said.