LAS VEGAS -- Few dispute Floyd Mayweather Jr.'s talent. Flashy and skilled, Mayweather is a supreme boxing technician with undeniable ring intelligence and sublime defensive skills.
He was reared from the crib to be a fighter -- his father, Floyd Sr., was a top professional; uncle and trainer Roger Mayweather was a two-time world champion; uncle Jeff Mayweather was also an experienced pro. In 1996, Mayweather claimed an Olympic bronze medal (after being robbed, many believe, in the semifinals), and he has won world titles in five weight classes from junior lightweight to junior middleweight.
He is a lock first-ballot Hall of Famer who reigned as pound-for-pound king for several years until Manny Pacquiao seized the mantle by battering a series of notable and naturally bigger men to earn the position during Mayweather's short-lived retirement in 2008 and part of 2009.
Yet, for all the glory, there remains a glaring weakness on Mayweather's résumé, one legions of critics point to most often when he goes off on a rant about being the best fighter of all time -- the less-than-challenging opposition he has elected to face since entering a strong welterweight division in 2005.
"I got respect for Sugar Ray Robinson. I've got respect for Muhammad Ali," Mayweather said. "But I'm a man just like they're men. I put on my pants just like they put on their pants. What makes them any better than I am? Because they fought a thousand fights? In my era, it's totally different, you know? It's pay-per-view now, so things change. It's out with the old and in with the new. Things change.
"Like I said, Muhammad Ali is one hell of a fighter. But Floyd Mayweather is the best. Sugar Ray Robinson is one hell of a fighter, but Floyd Mayweather is the best."
The notion is sacrilege to many, especially because although Mayweather makes the boasts, his strength of schedule simply does not back it up.
Mayweather, however, has a chance to at least shush the critics now that he is finally going to face an elite welterweight in champion Shane Mosley, whom he meets in the year's biggest fight so far on Saturday night (HBO PPV, $54.95, 9 ET) at the MGM Grand Garden Arena.
"He had to fight somebody if he wanted to be considered the best," said Mosley (46-5, 39 KOs), a two-time welterweight champion, three-division champion and pound-for-pound list stalwart.
Mayweather said the criticism is unfounded. He said it's not his fault he is so dominant that he makes the wins look easy.
"When I fight guys who they say will give me a tough fight, I can't help that the fight is so one-sided the fight is boring. That's not my fault," he said. "It's just that I'm that good. That's not my fault. You got some fighters that's talented. You got some fighters that are God-gifted. You got some athletes that's God-gifted. I just happen to be one of those athletes that's God-gifted. That's no different than Kobe Bryant or LeBron James."
When Mayweather was a junior lightweight, he beat the best and he did it easily in dominant TKO victories against Genaro Hernandez and Diego "Chico" Corrales.
In Mayweather's first fight at lightweight, he won the title by taking a tight decision from the No. 1 guy, champion Jose Luis Castillo. Then he outpointed Castillo again in a rematch.
But since then, it's hard to look at Mayweather's résumé and find that he has faced the best in his division.
At junior welterweight, Mayweather (40-0, 25 KOs) didn't fight the top opponents, leaving the division after an expected one-sided thrashing of Arturo Gatti in mid-2005 to claim a belt he never defended.
When he arrived at welterweight in late 2005, the division was stocked with talented potential opponents: Mosley, Antonio Margarito, Miguel Cotto and later Paul Williams and Pacquiao, just to name a few.
All of them have faced at least one other man on the list, but Mayweather didn't fight any of them, earning the ire of many fans.
Mosley, for example, lost a tight decision to a prime Cotto in 2007, then upset Margarito -- a man many accused Mayweather of ducking -- with a dominant ninth-round knockout to win a second welterweight title in January 2009 (Mosley's most recent fight).
But Mayweather never even pretended to be interested in any of them. Instead, these are the fighters he has faced at welterweight:
• Faded former junior welterweight titlist Sharmba Mitchell in a monumental mismatch.
• Former undisputed champion Zab Judah, who was coming off a loss to journeyman Carlos Baldomir.
• Baldomir, the utterly outclassed but legitimate champion at the time, whom Mayweather understandably faced so he could claim the lineal title.
• Ricky Hatton, the junior welterweight champion who was coming up in weight and had struggled in a previous trip into the division.
• Juan Manuel Marquez, the lightweight champion who jumped up two weight classes to fight Mayweather in the latter's September comeback bout. For that fight, Mayweather, who already had every conceivable advantage, still came in over the contract weight. (Mayweather also fought a fading Oscar De La Hoya in a massive money junior middleweight title bout in 2007, winning a more-difficult-than-expected split decision.)
"He's fought lightweights and junior welters who move up to the welterweight division," Mosley said. "The guys I fight jump into the ring [at] 172 [pounds]. The guys he fights jump into the ring 145."
Mayweather had never really expressed interest in facing Mosley despite his stature. But after years of belittling Mosley, Mayweather was more or less backed into a corner. After negotiations with Pacquiao failed in January and Mayweather was left without any other big-name opponents, Mosley emerged as the only plausible fight when his unification fight with Andre Berto, scheduled for late January, was canceled unexpectedly because of a Berto family tragedy.
"As a welterweight, he hasn't fought another top welterweight, and I'm the first one that's he fought so it makes the fight a big fight," said Mosley, who has made a living out of facing all comers, including De La Hoya, Vernon Forrest, Winky Wright, Margarito and Cotto, all when they were in or near their primes. "All the other guys have not really been the best, if you will. There are a lot of great welterweights out there that he could have chosen to fight instead of fighting the ones that he fought."
Despite the storm of criticism, Mayweather, guaranteed $22.5 million plus a percentage of the pay-per-view take Saturday, always brushes it off.
"They say I pick and choose who I fight," he said. "It doesn't matter. I'm Floyd Mayweather, and they come to see me regardless.
"Shane is a solid welterweight with great accomplishments, but I have been fighting these kinds of fighters my whole career without much appreciation. No one gives me credit for who I have fought during my career. From early to now, look at the opponents I have faced and see where they were when they faced me in the ring."
One of those defenses of Mayweather's previous selection of welterweight opponents -- to a point -- is from a surprising source: Naazim Richardson, Mosley's trainer.
"It wouldn't surprise me if he handles himself well in there with a real welterweight," Richardson said. "This kid can fight. [But] he secured his thing first, which I agree with. You come into the boxing game, you secure your money, you get your title. You secure your thing first. Now we can take some chances. There were things they said negative about Oscar. 'Oscar's not fightin' nobody.' Oscar got all that s---, secured and then [fought everyone].
"Don't overlook Floyd's genius in the ring. The kid's a genius in the ring. When the cameras come on, he loses his mind, but he's a genius in the ring."
Then Richardson's defense of Mayweather slacks off.
"The problem," he said of Mayweather's boasts of being the greatest ever, "is it doesn't match up with the cockiness you see. If he was a quiet guy, you'd have no problem with who he fought or the way he fought them. But it doesn't match up when you start mentioning guys like Robinson and Ali. It doesn't match up.
"It's not that he hasn't done a great job, it's just that he fought in one direction and one area and then you compare yourself to these guys who fought any and everything. His work has been enough to consider him an outstanding champion. All that's been proven. But to say you're the greatest of all time, you better put in that kind of work. It would make more sense coming out of [Mosley] than him."
If Mayweather's opponent selection has been a bid to keep his perfect record intact, Mayweather isn't letting on.
"I don't think about the '0,'" said Mayweather, whose last loss came on July 22, 1996, in the Olympic semifinals in Atlanta. "I think about winning. Everything takes care of itself if you win. Of course it's a great thing to be undefeated, but I don't consciously think about it when I'm preparing for the next fight."
Said Roger Mayweather, "Floyd knows how to win. Obviously, he doesn't know how to lose."
Floyd Mayweather is well aware of his record, repeating it often. But maybe Mayweather isn't aware that at least three other all-time greats were 40-0 before suffering their first defeat: Robinson, widely considered the greatest fighter ever (Mayweather's opinion notwithstanding), George Foreman and Felix Trinidad.
Mosley, who will earn a guaranteed $6.75 million plus a piece of the pay-per-view profits in a fight expected to easily exceed 1 million buys, doesn't put much stock in Mayweather's perfect record, mainly because of whom he has faced in recent years.
"I think there is too big a deal being made about the fact that Floyd is undefeated," he said. "Before my first loss, I was 38-0 with 35 KOs. That's a hell of a record, but that didn't mean I couldn't be beat, and it doesn't mean Floyd can't, either."
Whatever happens, Mosley is practically giddy that Mayweather finally stepped up to the plate.
"I definitely have to give him props for jumping in the ring with me and making this fight happen," Mosley said. "It's a big fight, and he stepped up and took it. Maybe I didn't get as much as I should have gotten, but I got a lot and it's good enough for me."
Good enough too, perhaps, for those who have appreciated Mayweather's immense talent and only wanted to him to face the welterweight best.
That happens, at long last, on Saturday night.
Dan Rafael is the boxing writer for ESPN.com.