"The Answer" to BJ Penn's dominance in the lightweight division came in the form of a historic upset at Abu Dhabi, United Arab Emirates.

Frankie Edgar of New Jersey upset Hilo's Penn by unanimous decision to win the UFC lightweight world championship yesterday.

The bout was a co-main event of the "UFC 112: Invincible" mixed martial arts show.

Edgar, who is nicknamed "The Answer," was considered a significant underdog, with some online gambling sites listing Penn as an 8-to-1 favorite.

It was also the first time since 2002 that Penn lost a lightweight (155 pounds) bout.

"This is it," Edgar said. "He's the greatest champion ever and I just beat him. I just hope I can be half the champion he was."

The five-round bout turned into a battle of jabs, with Edgar using an effective stick-and-move attack to stymie Penn.

The three judges scored the bout 50-45, 48-47 and 49-46 in favor of the challenger.

Edgar improved to 12-1 after winning his first world title bout. Penn, who had been 5-0 in his last five UFC lightweight bouts, dropped to 15-6-1. Penn was making the fourth defense of his lightweight title.

The first round featured numerous jabs from both fighters, and no takedown attempts. Penn had a bruise under his left eye at the end of the round.

The second and third rounds were similar to the first, with both fighters opting to stand and trade jabs. Edgar got a takedown midway through the second round, but it did not amount to much as Penn immediately got back to his feet.

After the third round, Penn was instructed by his corner to attempt a takedown. However, both fighters remained standing in the fourth round, with the jab-fest continuing.

Edgar scored another takedown in the fifth — and final — round, but Penn was able to quickly scramble back to his feet. Later in the fifth round, Edgar landed several effective punches to Penn's face.

Penn closed the fight with a flurry, but appeared exhausted as the final horn sounded. When the bout ended, Penn had bruises under both eyes.

Mark Munoz of California defeated Maui's Kendall Grove via second-round TKO in a middleweight bout on the undercard.

Grove dominated the first round, dropping Munoz with an uppercut and attempting several choke holds.

However, Munoz survived the first round and then gained control in the second round. Munoz worked his way on top of Grove, and then utilized a ground-and-pound attack to finish the fight. The referee stopped it at 2:50 into the second round.

Munoz improved to 8-1, while Grove dropped to 13-7-1.

In the other co-main event, Anderson Silva defeated fellow Brazilian Demian Maia by unanimous decision to retain the UFC middleweight (185 pounds) world championship. Silva dominated the five-round bout, but was roundly booed when he elected not to force the action the final two rounds.

In another featured bout, Matt Hughes of Illinois defeated Brazil's Renzo Gracie via third-round TKO.

It was the first UFC event ever staged in the Middle East region of the world.