LAS VEGAS – Where’s the power?

Floyd Mayweather Jr. and Manny Pacquiao, who fight one another tonight at the MGM Grand, are justifiably celebrated as two of the best fighters of their generation and perhaps beyond.

They don’t give the fans what they crave most, though: knockouts. At least not in the past several years.

Since 2010, Mayweather and Pacquiao have fought a combined 16 times but have only one knockout victory. And that knockout, by Mayweather in 2011, was primarily the result of Victor Ortiz looking away at the time the punch landed.

Why so few stoppages?

In Mayweather’s case, perpetually brittle hands might play a role. He evidently is not able to let loose quite as much as he did when he was younger for fear of injury. And, of course, “Money” is primarily a technician.

A more significant reason for the power outage probably is the natural size of the fighters.

Pacquiao is a small guy. He weighed 106 pounds as a 16-year-old for his first fight and has moved up a remarkable 10 weight classes, including his junior middleweight fight against Antonio Margarito in 2010. And Mayweather isn’t big either. THE RING junior middleweight and welterweight champion started at 130 pounds.

Pacquiao had tremendous power at 140 pounds and below, at which he had a record of 49-3-2, with 37 knockouts. He’s 8-2, with one knockout (Miguel Cotto), since. Mayweather also had great power once upon a time. He started his career 15-0, with 13 stoppages, and was 35-0, with 24 KOs. Since then, he’s 12-0, with only two knockouts (Ricky Hatton and Ortiz).

Trainer Joel Diaz believes Pacquiao’s natural size has played a particularly significant role in recent years.

“The welterweight division isn’t his division,” Diaz said. “His pop just isn’t as devastating against a bigger man. I think Pacquiao is a 140-pounder, 135 or 140. As you can see he came in (for tonight’s fight) at 145 and he ate breakfast before that. That means he weighed 143 the morning of the weigh-in.

“So his punches against a bigger man just don’t have the same effect.”

Diaz said that theory also applies to Mayweather (who weighed 146) to some degree but he believes “Money” has a size advantage.

“I think Mayweather will hurt Pacquiao because he’s the bigger man,” he said. “Mayweather is so accurate with his right hand. I watched every one of his fights against southpaws and he’s very accurate with his right.

“Every time Pacquiao lunges in, he exposes himself to the right hand. Juan Manuel Marquez timed him. And Mayweather is much smart and more accurate than Marquez.”

Trainer Abel Sanchez agreed with Diaz.

“Mayweather and Pacquiao are fighting bigger guys now,” he said. “They’ve matured enough to know that they have to rely more on their boxing. And if the KO comes, it comes. It’s not that guys lose power. It’s that the bigger guys they’re fighting can absorb the power because they’re used to taking punches like that.”

That concept applies to the vast majority of fighters but not all of them.

“Some guys – Edwin Valero was one of them – were just born with that heavy-handed, raw snap power that moves up in weight with them,” Sanchez said. “Roberto Duran was another one. Thomas Hearns. He had good leverage, nice length, and always threw that snap punch. He had light heavyweights going down.

“Mayweather and Pacquiao aren’t like that.”

Their records bear that out.