LAS VEGAS » Saturday night was supposed to be the defining moment in B.J. Penn's career.

Two current champions went head-to-head in the most heavily promoted fight in UFC history. Penn had an opportunity to hold two UFC belts at the same time, something that has never been done.

Instead, it was Georges St-Pierre that ascended to the top of the MMA world with a TKO victory over Penn in a one-sided fight that was brutal and unforgiving.

In some cases, the way a fighter performs in a fight can be just as important as getting a win or a loss. Stephan Bonnar lost to Forrest Griffin in one of the first fights ever shown on cable television, but the way he went blow-for-blow with Griffin for 15 minutes made him an instant star in the sport.

It wasn't a surprise that Penn lost to St-Pierre on Saturday night. He was a clear underdog going into the fight.

But the way in which St-Pierre tore through Penn was. Penn's striking was considered to be superior going in, but St-Pierre's was better. Penn is a world champion in Brazilian jiu-jitsu, but St-Pierre did what he wanted on the ground, passing Penn's guard at times as if it was nonexistent.

To pour salt in the wound, the fight was stopped once Penn couldn't answer the bell to start the final round. It's disputed whether the ringside doctor advised referee Herb Dean to stop the fight, or if Penn's corner had decided their fighter had enough.

Either way, Penn was put in a position he had never been before. Battered, beaten, bloodied and outclassed in a sport he is considered one of the pound-for-pound best.

But even with all that, he's still the UFC lightweight champion. Even with every St-Pierre elbow that pounded Penn's face, his status as the best 155-pound fighter in the world remains unchanged.

Kenny Florian has an opportunity to prove otherwise as the next challenger to Penn's title. It's unclear when the fight will take place. Penn fights about three times every year, suggesting it could be sometime in May or June.

It'll be a long time before Penn jumps back up to the welterweight division. UFC President Dana White said as much during Saturday night's post-fight press conference.

“;I don't think I'll have to encourage him (not) to do that,”; White said.

Now, Penn has no choice. Relegated to the division that he has dominated since dropping back down in weight over two years ago, he can prove his superiority at 155 pounds.

His legacy can be as the greatest fighter ever to compete at 155 pounds by ripping through challengers one-by-one.

It'll take time for Penn to get over Saturday night's humbling experience. Some fighters have taken a beating like he did and lost their edge both physically and mentally, never returning to their previous glory.

How he is remembered will be determined over the next six months. He could forget the valuable lessons he's learned since turning 28. He could lose the dedication he's made to fully devote himself to mixed martial arts.

He could go back to Hilo, raise his newborn daughter, and never worry about trying to be the greatest fighter of all time.

Or he can remind everyone he's the best at 155 by tearing through Florian this summer.

That will be what defines the Prodigy.