Photo by Naoki Fukuda

LAS VEGAS – The stakes are high for both Floyd Mayweather Jr. and Manny Pacquiao on Saturday night at the MGM Grand.

The winner of the fight of the 21st century can legitimately claim that he’s the best fighter of his era, perhaps the best since Roy Jones Jr. in the early 2000s. In other words, an undisputed king will be crowned.

Make no mistake, though: Mayweather has much, much more to lose than Pacquiao.

If Pacquiao loses? Not a big deal. He has lost five times before, three times by knockout. And he’s the underdog against Mayweather. He is expected to lose. His legacy will have taken a relatively minor hit, although the degree depends on how he loses.

If Mayweather loses?

The world’s No. 1 fighter told reporters on Tuesday that his motivation now is more about money than the “0” in his loss column. That’s believable given his love of ridiculously expensive things but only to a point. He still cherishes his perfect record even if he won’t acknowledge it. That’s clear.

If Pacquiao has his hand raised, the “0” becomes a “1” and Mayweather will never be seen the same again.

“I don’t think there’s any doubt about it,” said Associated Press columnist Tim Dahlberg, who has covered boxing since 1979 and knows Mayweather well. “Mayweather has got his ‘0’ to lose and that’s very important to him. Not only that, he considers himself the best ever mainly because he’s 47-0. If he’s 47-1, he can’t really make that claim.

Photo: Gabriel Buoys/AFP-Getty

“That’s very important to Mayweather. He takes a big tumble if he loses.”

It’s hard to be overly critical of Mayweather to this point.

He has fought most of the best possible opponents in and around his weight and remains unbeaten. On top of that, few of his fights have been competitive. No one has even approached his skill level.

Mayweather doesn’t have defining fights, though, which has always been a prerequisite to being considered truly great. Ali had Frazier and Foreman. Leonard had Hearns, Hagler and Duran.

Who has Mayweather had? Oscar De La Hoya? De La Hoya is a big name but was considered on the downside of his career when they fought. Juan Manuel Marquez? Miguel Cotto? Shane Mosley? They all came in with distinct disadvantages.

No, Manny Pacquiao is his defining fight.

It’s almost as if Mayweather is putting the bulk of the boxing capital he has earned the past 20 years on red in roulette. If he wins, he benefits from a windfall. If he loses, he takes an enormous, painful hit. This fight is a big, big gamble for him even if you believe that Pacquiao has slipped to some degree.

Of course, the depths to which Mayweather would fall with a loss also depends on how he loses.

If he ends up on the wrong end of a close, perhaps controversial decision, then the damage, while still considerable, wouldn’t be quite as devastating. And perhaps a rematch could be arranged, which would provide an opportunity to recoup some lost prestige.

If he loses badly – by knockout or one-sided decision – then he crashes to earth in a fireball that will be seen worldwide.

Yes, he would still be perceived as a gifted boxer and will one day be inducted into the International Boxing Hall of Fame. That’s set in stone no matter what happens the rest of his career. He just would no longer have a superhuman quality.

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“I think people would view him as a fighter who has been exposed, who really wasn’t that good to begin with, a fighter who perhaps handpicked his opponents. I think a loss would be devastating to Floyd,” Dahlberg said.

Pacquiao?

If he loses a close, competitive fight, then he could be celebrated just because he will have defied expectations. That also would give him leverage in his pursuit of a rematch, assuming he would want one.

If he is blown out, he will have squandered the biggest opportunity of his career but at least it will have been anticipated. The vast majority of those who know boxing believe Mayweather will win.

And Pacquiao will always have his remarkable series against the great Mexican trio of Marquez, Erik Morales and Marco Antonio Barrera, his defining fights, no matter what happens from here on out.

“If this is a bad fight, if Pacquiao just kind of chases him around, throws wild punches and does nothing, then Pacquiao will be seen as a very good fighter who couldn’t come through when it really counted in the biggest fight of his career.

“But if he loses a really good fight, a split decision, an action packed fight, Pacquiao is just as big as he is now if not bigger. More important to him, back home, it’s very important to the Filipino people that he puts up a great fight.”

So, obviously, there is pressure on both fighters  just a lot more on Mayweather.