Shane Mosley beat Oscar De La Hoya twice in major championship fights, taking the welterweight title from him in a stirring 2000 battle and then controversially winning the junior middleweight title from him in 2003.

Back then, they were respectful ring rivals. Today, Mosley is a partner in De La Hoya's Golden Boy Promotions and they've become pals. In an individual sport, they've become as close to being teammates as you can be.

That's why, in a highly unusual move for a superstar fighter, Mosley has agreed to serve as De La Hoya's chief sparring partner during his preparation for the May 5 mega-fight (HBO PPV) with Floyd Mayweather Jr.

A boxing star has his own sparring partners. A boxing star doesn't serve as a sparring partner, especially not to a boxer he has beaten twice.

But Mosley, whose speed, size and skills are about as close to Mayweather's as anyone else's in boxing, is not your typical star fighter.

He's down-to-earth and loves training. He's more than happy to do what it takes to help De La Hoya, especially because of how big a victory would be for the company they both have a stake in.

"That's what partners are for," Mosley told ESPN.com. "Whatever I can do to help, I will do. I want Oscar to have all the advantages he can in the fight."

Mosley, who has a knack for being able to imitate just about any style you can think of, will report to De La Hoya's Puerto Rico training camp April 1 and spend the month there sparring regularly with De La Hoya.

"I will help Oscar out and keep myself in shape as well," Mosley said. "I'm probably the closest thing fighting to Mayweather right now, so it will be a good advantage for Oscar to work with me. I will get some fight tapes and study Mayweather and his style. I will be able to imitate him and help Oscar dismantle Mayweather."

De La Hoya is already in camp and didn't want to discuss it, but the idea was hatched a few months ago when Golden Boy matchmaker Eric Gomez, also one of De La Hoya's best friends, was trying to come up with a list of possible sparring partners.

"I had discussions with Oscar about who can help him because there really isn't anyone out there that fights like Floyd," Gomez said. "He's the best technician in the game and he has the combination of speed and technical skills. It kept popping into my mind that the closest to him was Shane. So, I told Oscar that I had come up with the best possible sparring partner."

And when Gomez sprung the idea of Mosley on him?

"He liked the idea," Gomez said. "He's been in there twice with Shane and they fought and sparred in the amateurs. Shane has given him problems before. I think that Shane can imitate anybody. It clicked right away."

Getting Mosley on board was easy. A couple of months ago, Gomez simply asked him if he was interested.

"[Mosley] genuinely loves boxing and loves to train. He said, 'I will give it a try,'" Gomez said. "I called him one day a while before his own fight [Feb. 10 against Luis Collazo] to ask him. The worst thing he could do is say, 'No.' So I asked him, 'How would you feel about sparring with Oscar?' He said, 'I would love to. It would be great. I wouldn't mind going down to Puerto Rico.'"

Said Mosley: "I told him, 'Just tell me when to come and I will be there.'"

When he spars with De La Hoya, Mosley understands it is strictly to help De La Hoya.

"I will try not to make it competitive. I don't want it to be competitive," Mosley said. " This is for Oscar's benefit. I will not try to outshine Oscar because this is not about me. I'm going to do what I can do to imitate Mayweather. I will make it difficult for Oscar to hit me, like Mayweather will."

Gomez is pleased with the arrangement.

"I think Oscar will get his best looks from Shane," he said. "It's friendly and helpful, but you know how boxing is -- it's competitive. There will be some heated sparring sessions whether you like it or not. But I think there is enough professionalism in there that they won't be too competitive. And [trainer] Freddie Roach will be there. But there are days when they will have to go hard at each other."

It's a good bet that some of the action will be captured by HBO's cameras, which have been granted access to the both training camps for "De La Hoya/Mayweather 24/7," a four-part countdown series premiering April 15.

It won't be the first time Mosley will be helping De La Hoya get ready for an important event. Mosley also sparred with him as he was getting ready for a run to the 1992 Olympic gold medal.

"I will do whatever is needed of me," Mosley said. "We're there to work. I'm not going down there to overwork him, though. I want him to be the best he possibly can be for Mayweather. I will tell him things I see when we're in the ring. I'm definitely going to be a help."

Although De La Hoya will cover Mosley's expenses, Mosley said he won't accept a salary for the work.

"We're partners. I don't need to be paid," Mosley said. "Besides, I will get good work, too. I get to spar with Oscar De La Hoya, and that will help keep me sharp."

Gomez admitted that when he first thought of the idea, it made him chuckle.

"I was picturing 'Rocky III,' where Apollo Creed helps Rocky," Gomez said. "It's similar to the movie. I was thinking, 'How funny would that be if Shane agrees to do it?' I thought it will be like the movie. Apollo and Rocky fought twice and then Apollo ends up helping Rocky get ready to fight the next young kid."

It's not lost on Gomez that Rocky, with Apollo's help, did wind up defeating Clubber Lang. The whole Golden Boy crew is hoping life imitates art.

Dan Rafael, ESPN