PHILADELPHIA -- When B.J. Penn commits to being his best, there isn't a lightweight in the world capable of defeating him.
Kenny Florian learned that painful lesson on Saturday at UFC 101.
Penn put on a performance that will not soon be forgotten. He dominated Florian from the opening round until the 3 minute, 54 second mark of Round 4, when his rear-naked choke finished matters.
There wasn't a flaw in Penn's game, and 17,411 fans inside Wachovia Center watched in amazement as he methodically picked apart every aspect of Florian's fight plan. He controlled the standup with solid rights that neutralized Florian's 4-inch reach advantage and resulted in two first-round knockdowns.
Penn also stopped all of the challenger's takedown attempts. And when they hit the ground, Penn showed no sign of wear and tear. His cardio was the best it had been in years, which helped lead to the submission hold.
For the first time in a long time, Penn came fully prepared to fight. Penn had no other choice if he wanted to retain his title.
Florian was more than equipped to win. He had improved every aspect of his game.
Florian's jiu-jitsu and Muay Thai skills had reached new heights. He'd become proficient in boxing, but most important, Florian was confident Penn was ripe for picking.
Penn knew months in advance that Florian was a formidable opponent. So he packed his bags, left his family in Hilo, Hawaii, and headed to California to train with brothers Nick and Nate Diaz.
The sparring sessions were vigorous, the workouts tiresome, but Penn never backed off. The result was immediately noticeable on fight night.
"B.J. Penn looked better physically than I've seen him since 2001," UFC president Dana White said. "He came out and fought an amazing fight against a highly motivated and talented Kenny Florian."
The moment Penn stepped in the Octagon it was clear that he'd taken no shortcuts in training. Over the past few years, training has not been one of his favorite undertakings. Leading to this fight, however, Penn put in the work.
Rededicating himself didn't come overnight. He did some soul-searching immediately after his TKO loss in January to welterweight champion Georges St. Pierre, and concluded that he was cheating himself and his fans.
Shortly thereafter, Penn was on a mission to prove that he is still by far the best lightweight mixed martial artist alive. He wanted to make that point loud and clear against Florian.
"This fight was very important," said Penn, who improved to 14-5-1. "After you get a loss like I had it was very important to come back.
"I wasn't used to going places and having the fans booing me. I really wanted to come back and show everybody that I am a fighter, that fighting is my life."
Mission accomplished. When Florian (13-4-0) tapped, the crowd cheered wildly; Penn had regained their respect. He had officially returned to his old self, and in what better state to do so than Penn-sylvania?
This was Penn's night; his comeback party. But he doesn't want the celebration to end anytime soon.
"The great thing about the 155-pound division is how stacked it is," White said. "And I think Diego Sanchez is probably next in line for a title shot against B.J. It's a great fight."
The buildup will be great. Sanchez is a confident fighter who has been campaigning for a title shot since moving down to lightweight this year. Sanchez (23-2-0) has fought twice at 155 pounds and has looked impressive, but he will have all kinds of problems with the Penn who fought last night.
If Sanchez is to pull off the upset, he will need some help from the champion. Penn would have obliged last year, but not now.
Before coming to the arena Saturday morning, Penn recalled his younger days when he dreamed of becoming a mixed martial artist. It added fuel to his fire and gave him that extra boost against Florian.
"I woke up and asked myself, 'nine years and I'm still doing this to myself? What the hell am I doing?'" Penn said. "Then I thought back to when I was a teenager, 17, 18 years old; that was my dream to fight in the UFC and be a champion.
"I wanted to go out there and have fun, live my dream tonight. That's really what I wanted to do."
It's exactly what he did. Now Penn wants to continue having fun, but he must remain dedicated to working hard in camp. After the success he experienced last night, there is little chance Penn will revert to his old ways.
He will continue to prepare diligently. There is too much at stake.
"Why would I change anything? Being in the sport so long, it seems like these young guys are passing me by," the 30-year-old Penn said. "You have to stay on the cutting edge, otherwise you are old news."
Franklin McNeil is an analyst on ESPN.com's "MMA Live."