Sergio Mora (right) is taller and naturally bigger than Shane Mosley. Photo / Gene Blevins-Hoganphotos-Golden Boy Promotions

LOS ANGELES — Shane Mosley was the toast of boxing only two fights ago, when he stunned almost everyone by brutally knocking out Antonio Margarito in February of last year at Staples Center.

The upset dispelled any notion that the future Hall of Famer was in decline even though he was 37 at the time and earned him a shot at Floyd Mayweather Jr., who some believed he could beat.

Alas, Mayweather won almost every round and Mosley — in spite of all he’s accomplished — is back to where he was before the Margarito fight: Perceived to be a has-been whose days in the sport are clearly numbered.

Only this time there will be no victory over Margarito to change the minds of the masses. Instead, he faces Sergio Mora on Saturday night in same arena in which he beat Margarito, a fight he’s expected to win in spite of advancing years.

If he loses, retirement might be a good option. If he wins, it’s only Sergio Mora. Naazim Richardson, Mosley’s trainer, said this is a can’t-win situation if there ever was one.

“I’d have to go on a private tour to convince people how good Sergio Mora is,” Richardson told RingTV.com. “It’s not going to happen. I had a fighter named Bernard Hopkins. He fought a kid named Enrique Ornelas, who is a monster. I knew once he beat Ornelas that he wouldn’t get credit. And he didn’t. This is the same situation.

“The people in boxing know Mora is a beast. The people who don’t know will say, ‘Oh, he’s just one of the Contender guys.’ Shane won’t get full credit.”

Beast might be a strong word for Mora but most experts see him as a legitimate threat to Mosley.

The native of Los Angeles has the wrong style for Mosley, who’s at his best when his opponent comes directly to him (as Margarito did). Mora is no Mayweather but he’s a good, athletic boxer. He’s taller and naturally heavier than Mosley. And he once beat Vernon Forrest, who twice outpointed Mosley.

The only mark against him is a perceived lack of power. Mora (22-1-1) has only six knockouts.

Still, if this fight took place five years ago, no one would’ve given Mora a chance. Mosley, who has been fighting for more than 30 years, turned 39 on Sept. 7 and is coming off the worst performance of his career.

“I understand that people have questions about me,” Mosley said. “People could say, ‘You had Mayweather out [in the second round] and should’ve knocked him out. You lost every round after that.’ Mayweather was the better man that night and we just move on.

“ÔǪ I have something to prove to myself and the fans.”

So he does have questions in his mind?

“No, not really,” Mosley said. “It’s just about proving it to the fans. I have no doubt that I can be the best fighter out there. This fight is going to get me back on track.”

The fact Mosley has to prove anything to anyone after a 17-year career in which he has held five titles in three weight classes — and is one fight removed from a spectacular victory — is unfortunate.

Mike Tyson was shot when he faced Lennox Lewis in 2002 yet many fans, blinded by Iron Mike’s fearsome, bigger-than-life aura, were certain he’d knockout the big Briton. When the opposite happened, they had a hard time figuring it out.

Mosley is no Tyson. He’s recognized as a great fighter but even if he established something resembling an aura against Margarito, it disappeared against Mayweather.

That has been Mosley’s lot in a sport whose fans are particularly fickle.

“I think any time you come off a loss and you’re Shane’s age, some questions will arise,” said Judd Burstein, Mosley’s longtime advisor. “ÔǪ He’s always had that unfortunate aspect to his career, though. He’s always been a gentleman, not a controversial figure.

“So I think he lives and dies by the quality of his fights and not by the force of his public persona.”

Mosley has big plans if beats Mora. Manny Pacquiao is at the top of his wish list and that seems to be more likely in light of Mayweather’s legal problems. Yes, the man thinks big. Another possibility is a rematch with Miguel Cotto.

Even if he loses, the thought of retirement might cross his mind but probably will keep right on going. He has said many times that he sees himself fighting into his 40s, as Hopkins has. Mosley, who shares a fanaticism for fitness with Hopkins, said was back in the gym three or four days after the Mayweather setback. Burstein called him “a freak” in that regard.

Mosley can still command a sizable payday; he’s guaranteed $1 million for the Mora fight. And, perhaps most important, he still enjoys it. He truly loves the sport.

“I can’t imagine being away from boxing,” he said. “I would probably have to force myself to leave. I think in three, four years I should be done; I should be ready to force myself to leave. My son [boxer Shane Jr.] is coming up. I’ll start getting behind him.

“The young guys can’t beat me. Why stop? When I start getting beat by guys nobody knows I’ll know it’s time to hang up the gloves. Now, I’m having too much fun. I feel like I’m getting my second wind ÔǪ maybe my third.”

The Mora fight sure doesn’t seem like a no-win situation in Mosley’s mind.

Michael Rosenthal can be reached at [email protected]