Shane Mosley, the former three-division world champion, has heard it before -- that he is too old and doesn't have much of a chance to win.
That was the conventional wisdom as he prepared to fight then-welterweight titleholder Antonio Margarito in January 2009. Mosley was coming off a shaky performance in a 12th-round knockout of Ricardo Mayorga, and, before the Mayorga fight, Mosley had suffered a decision loss to Miguel Cotto (albeit a highly competitive one) in a welterweight title bout.
So what happened to underdog Mosley against Margarito? He only destroyed Margarito, who had been stripped of the loaded hand wraps he had been caught trying to enter the ring with.
Mosley looked great that night, beating down supposedly indestructible Margarito and knocking him out in the ninth round. The California native proved that he was, by no means, a spent bullet.
Mosley, however, finds himself in a similar position again as he heads into his showdown with pound-for-pound king and welterweight titlist Manny Pacquiao on Saturday night (Showtime PPV, 9 p.m. ET, $54.95) at the MGM Grand Garden Arena in Las Vegas.
The reason is simple: After the big win against Margarito, Mosley couldn't continue his top-level performances. Although Mosley briefly hurt Floyd Mayweather Jr. in the second round of their fight last May, it was his only moment of consequence in the fight.
Mayweather easily outboxed Mosley to win a near-shutout decision. Mosley looked old and slow and was unable to get off many punches in the resounding defeat.
Next came an unwatchable draw against Sergio Mora in a September junior middleweight bout. Most ringside observers thought Mosley had pulled it out, but it still wasn't the kind of performance that impressed anyone.
If anything, it was another example of just how far Mosley has slipped since his dazzling early-2000s prime, when he was welterweight champ for the first time and widely considered the No. 1 fighter on the pound-for-pound list.
Mosley, who had pleaded for a fight with Pacquiao for the past few years, finally got it, but he is the first to admit that his performances against Mayweather and Mora left a lot to be desired. Mosley is realistic about those fights, understanding that his vulnerability is one of the key reasons that Top Rank promoter Bob Arum extended him an offer to face Pacquiao, his cash cow.
"I don't think [Mayweather or Mora] will have anything to do with what I do against Pacquiao because styles make fights," Mosley said. "But if it wasn't for those two fights, I probably wouldn't be here today. So those fights were needed."
Still, Mosley, 39, has been a determined fighter throughout his career. He said he is using his underdog status to help motivate himself against Pacquiao.
"I don't care that people are saying I'm an underdog or not," Mosley said. "What matters is what happens in the ring. It only matters what happens [Saturday]. That's the only thing that matters.
"Watch and learn. I will prove people wrong."
Arum has ignored critics who have harped on Mosley's recent performances, saying his goal was to bring an entertaining fight to boxing fans against a well-known opponent.
"The reason Shane was selected for this fight is because we know that we are in the entertainment business and we know that Manny Pacquiao against Shane Mosley will be one hellacious and entertaining fight," Arum said. "We picked Shane to fight Miguel Cotto a couple of years ago and to fight Antonio Margarito a couple of years ago. Shane is an all-action fighter, and when he is in with a guy who is an action fighter, as well, you are going to see fireworks and a real exciting fight."
Entertainment value aside, Arum is also selling Mosley (46-6-1, 39 KOs) as a serious threat to Pacquiao (52-3-2, 38 KOs).
"Nobody can count Shane Mosley out," Arum said. "He is a good, good fighter, especially when he fights an aggressive opponent like Manny Pacquiao. Shane Mosley is a dangerous fighter. He is bigger than Manny, strong, and he still has his speed. He has never been stopped. He can take anyone's best punch and come back as strong as ever. He's so resilient. You can't hurt him."
Those are Arum's public sentiments, but it hasn't stopped him from already working on a fall fight for Pacquiao against rival Juan Manuel Marquez. In their two fights, Pacquiao owns a draw and a split-decision victory in fights that could have gone either way.
Arum has refused to discuss the offer made to Marquez in the midst of the promotion for Saturday's fight, but Mosley didn't sound too offended.
"That's fine," Mosley said. "Sometimes as businesspeople you have to look to make the next fight and the next fight. I think that's what makes Top Rank such a great promoter. That's for them to think that way and not for me to think that way. I have to think about [Saturday] and take care of [Saturday]."
Pacquiao is always busy in a swirl of activity outside the ring, even when preparing for a fight. Pacquiao has made numerous promotional appearances, saw the launch of his first music CD last week and has signed various endorsement deals.
Still, the Filipino icon and only eight-division titleholder in boxing history said he isn't looking past Mosley.
"Shane Mosley is still very strong, and he moves more like he's 30 years old," said 32-year-old Pacquiao. "He's the kind of fighter who is bigger than me. Pound-for-pound, he's still good.
"Shane can still fight. He's determined to shock the world."
Freddie Roach, Pacquiao's trainer, is also expecting a tough fight and said Pacquiao trained as if he would get one.
"We're 100 percent ready for the fight," Roach said. "If Mosley brings his best, we're ready for his best. I don't think there is any room for an upset, but in boxing you never know. We're 100 percent ready on our end. We've done everything we can to get ready for the fight.
"We're definitely looking at [video of] his best fights because we expect him to be at his best. The Margarito fight he looked great, and Margarito has an aggressive style like Manny and that's how we'll attack him. It will be a little more scientific, of course, but we're ready for the best Shane Mosley out there."
Naazim Richardson, Mosley's trainer, has worked with Mosley for his past few fights, and he worked with all-time great Bernard Hopkins for many years. Even though Mosley has had poor performances in his past two fights, Richardson is convinced his fighter can still summon one more big effort to dethrone Pacquiao.
Richardson noted that fighters such as Erik Morales and Hopkins, older fighters past their primes, put on outstanding -- and unexpectedly good -- performances in their last bouts.
Morales turned back the clock in a sensational battle against Marcos Maidana last month despite a majority decision loss. Hopkins was held to a controversial draw when he challenged light heavyweight champion Jean Pascal in December.
"Most of you saw the Erik Morales fight and most of you saw the Pascal-Hopkins fight, and we keep counting these guys out," Richardson said. "These aren't just old men who box. These are legendary fighters who have age on them now. There's a difference between a legendary fighter who has age and an old boxer. These aren't just men. When these guys were in their prime, they were exceptional. Michael Jordan could probably still come out now and make the starting five on any team in the NBA. We discount these older guys, but we forget these were special guys. When special gets old, you can still be extraordinary."
Richardson counts Mosley in the category of "legendary fighter with age on" and said he expects a big performance from Mosley on Saturday. He wants Mosley to get proper credit if he should pull the upset.
"When 'Sugar' Shane Mosley scores this incredible victory over Manny Pacquiao, I don't want Manny to be declawed or defanged," Richardson said. "I don't want people to reduce Manny into distraction. I don't want to hear that Manny is only 2 inches tall and weighs 32 ounces. I don't want to hear any of these things that I've heard.
"They say he's a killer and the most monstrous fighter out there today, so Shane should get his full amount of due when he pulls this victory off."
Mosley has done it before.
Dan Rafael is the boxing writer for ESPN.com. Follow him on Twitter @danrafaelespn.