The last time Floyd Mayweather Jr. lost, it took a Bulgarian conspiracy to do him in.

That was before a character named Money even existed, before Mayweather had earned his first dollar in the ring. He was 19 and cocky, fighting for his country, with the man who taught him everything he knew about boxing giving advice by phone from a Michigan prison. He boldly declared that he'd win if the gold wasn't stolen from him.

Unfortunately for Mayweather, his reading of Olympic history was correct. He lost a decision to a countryman of the Bulgarian in charge of Olympic boxing in the semifinals at 125 pounds that was such a robbery even the referee raised his hand in triumph, sure that Mayweather won.

"Politics, basically," Mayweather said. "But in a way I'm glad I got the bronze medal. It just made me work harder, made me want to become even more successful."

Fourteen years later, there's no more successful fighter around. Mayweather is not only a pay-per-view superstar who has made more millions than he can count, but — in his eyes, at least — one of the greatest fighters ever.

He returns to the ring Saturday night ready to earn many millions more in a 147-pound showdown, but this time there's a catch. In the other corner will be a fighter who some think has the best chance to beat Mayweather since the days he was fighting for medals, not money.

No, it's not Manny Pacquiao, much to the disappointment of many fight fans. But Shane Mosley may be the second-best thing.

"He couldn't just fight Joe Blow," Mosley said. "He had to fight somebody good if he wants to be considered the best."

That somebody is a fighter who has been in and won big fights himself, a fighter who brings both quickness and power to the ring. Mosley (46-5, 39 knockouts) may be aging chronologically, but he showed by stopping Antonio Margarito his last time out that he still has the speed and reflexes he used to beat Oscar De La Hoya not once, but twice.

The Margarito fight, though, was 15 months ago. Even without ring rust, 38-year-old fighters can sometimes look their age at just the wrong time.

Mosley weighed in Friday at the class limit of 147 pounds, while Mayweather was 146.

This may be Mosley's last chance to establish himself as one of the greats of his era. And while he's always in great physical shape, it may be the mental edge that proves most important as he tries to chase down the most slippery fighter around.

Judging from the subdued Mayweather and his camp at Wednesday's final prefight press conference, Mosley believes he has that edge. He will go into the ring trying not to just earn his $7 million guarantee, but the respect of boxing fans everywhere.

"My style can give him problems," Mosley said. "It's a different style from a lot of fights he's been fighting. He's going to have to adjust in the ring."

Adjustments have been the talk all week for a fight that promoters believe could end up being one of the top non-heavyweight pay-per-view events ever. The fighter who makes the right ones the soonest should have the upper hand, though the oddsmakers who make Mayweather a 4-1 favorite clearly believe he has the superior defensive skills to prevail.

If Mayweather slips and slides and backpedals his way around the ring it could be a long night for Mosley, which is one reason why his trainer, Naazim Richardson, has tried to goad Mayweather into trading punches. It could also be a long night for anyone who paid $59.95 and up to watch it on TV at home, but that's the chance taken with any Mayweather fight.

"No matter what happens I'm always in a no-win situation," Mayweather said. "All I've done over the years is constantly beat everyone they put in front of me, but I'm never going to get my just due. When I beat Shane they'll just say I beat an old fighter."

Indeed, the knock on Mayweather is that even though he won all 40 of his fights, he has picked his opponents and opportunities carefully. His biggest win was against De La Hoya, who had clearly slipped by the time they fought, and he backed away from a megafight with Pacquiao in a dispute over whether Pacquiao would undergo blood testing for performance-enhancing drugs.

It's hard to argue with his success cashing in on his boxing talents, though. Largely because he plays a bad guy named Money Mayweather on HBO's "24/7" series before his fights, Mayweather has parlayed his fame into pay-per-view sales that dwarf those of any fighter today.

And it's hard to argue with Mayweather skipping a Pacquiao bout to fight Mosley, considering this fight should sell so well that Mayweather will make even more than the $22.5 million he is guaranteed.

"I don't think about no Pacquiao," Mayweather said. "I'm a boss and I only talk to bosses. He has to learn to do numbers like I do. He's got to step his pay-per-view numbers up."

Ironically, Mayweather passed on a fight with a boxer who he suspects of doing performance-enhancing drugs to fight one who admitted to using them before his second fight with De La Hoya seven years ago. For the first time in boxing, both fighters have been subjected to Olympic-type testing, and both have been clean in blood and urine tests.

The Pacquiao fight could still be made, possibly for November, should Mayweather prevail as expected. If he doesn't, there's a rematch clause in the contract for a second fight.

Either way, Mayweather will live up to his Money nickname.

"It doesn't matter," he said. "I'm Floyd Mayweather and they come to see me regardless."