B.J. Penn successfully defended his lightweight title with a fourth-round submission of Kenny Florian in the main event of UFC 101: Declaration last night at the Wachovia Center in Philadelphia.

Penn (14-5-1) forced Florian (13-4) to tap out to a rear-naked choke at 3 minutes, 54 seconds of the fourth round, improving to 9-1-1 in his career in the UFC lightweight division.

“;The Prodigy”; reminded the world that despite a tough outing against Georges St-Pierre in January, he is still the most dominant fighter in the world at 155 pounds.

“;When I woke up this morning I thought, 'I've been in this thing for nine years. What the hell am I doing with myself?' “; Penn said. “;But this is my dream.”;

Penn's performance at his normal weight class, 15 pounds lighter than where he fought St-Pierre, showed just how different a fighter can look in a different division.

Florian entered the bout on a six-fight winning streak, but had nothing for the champion, who has won three of his last four fights at 155 pounds by the same submission move.

Penn was ahead on all three scorecards before ending the fight.

Nearly the entire bout the fighters stayed on their feet, with Penn fighting off every Florian takedown attempt.

Penn scored his first takedown in the fourth round and immediately went to work.

After falling into half guard, Penn bashed away at Florian's face before mounting the challenger.

After working his way to Florian's back, Penn eventually sunk in the rear-naked choke, forcing Florian to tap his hand repeatedly on his chest to signal he was done.

Penn came to the ring wearing a “;Penn State of Mind”; T-shirt to a chorus of cheers.

He ended the first round with a big punch that wobbled Florian, but the bell sounded before he was able to continue his onslaught.

The second was the closest Penn came to losing a round since his return to lightweight in 2005. Florian, however, was still unable to score a takedown of Penn, who had the three biggest shots of the round with two uppercuts and a counter right.

Penn's next title defense will likely be against Diego Sanchez.

Philadelphia Phillies outfielder Shane Victorino, who visited Penn earlier in the week to wish him good luck, was shown in the crowd, getting one of the biggest ovations of the night after flashing his Phillies World Series ring from last year.

Team Hawaii finished 1-2 for the night as both Kendall Grove of Maui and Shane Nelson of Hilo lost by unanimous decision.

All three judges scored the contest 30-27 for Brazilian Ricardo Almeida (11-3) against Grove (12-6). Grove nearly submitted the black belt in jiujitsu with an armbar in the second, but that was most of the offense he could muster.

Almeida put Grove on the defensive the entire fight with repeated takedowns and even showed off an improved standing game.

Nelson (13-4) ended up competing after Grove on the main card because his preliminary bout was pushed back due to time constraints.

But Aaron Riley (28-11-1) earned revenge for his last loss to Nelson, using his bigger frame to physically overwhelm his opponent, who had an eight-fight winning streak snapped.

In the co-main event, middleweight champion Anderson Silva (25-4) continued his undefeated UFC run with a first-round knockout of former light heavyweight champion Forrest Griffin (16-6).

The Associated Press contributed to this report.