LAS VEGAS – A thunderous roar erupted from the massive crowd at T-Mobile Arena on Friday as announcer Jimmy Lennon Jr. told the crowd that UFC lightweight champion Conor McGregor weighed 153 pounds for his Saturday bout with the unbeaten Floyd Mayweather Jr.

There will be an even more ear-splitting noise if McGregor can do what 47 previous Mayweather opponents weren’t able to accomplish and follows through on his prediction to knock out the 49-0 boxing savant in one of the first two rounds.

It’s been a while since there was legitimate excitement at a Mayweather fight.

He’s been so good, so head-and-shoulders above his peers, that his bouts have routinely been one-sided yawners in which the opponent struggles to land anything of significance.

One would have to go back to the Miguel Cotto fight in 2012 – which Mayweather won by scores of 117-111 twice and 118-110 – to find a fight which was exciting from start to finish and in which the opponent landed more than an every-now-and-then blow.

In his last six fights, there have been 216 scored rounds. Mayweather has gone 150-66, meaning he wins 70 percent of the rounds.

Will McGregor, making his pro boxing debut against one of the three or four best defensive fighters in the history of boxing, be able to change that narrative without getting picked apart?

If Mayweather has gotten old since his last appearance in the ring, when he routed Andre Berto in 2015, it could happen. On Friday, two bettors at MGM Grand wagered $100,000 apiece on McGregor to defeat Mayweather.

But though odds at some sport books creeped down to as low as 4-1, it seems the Mayweather money has begun to come in. On Friday, Mayweather was up to minus-600 and McGregor at plus-400.

Defense wins championships and Mayweather is the master defender. He’s tough to hit when he’s standing still directly in front of an opponent, let alone when he’s moving in the ring.

McGregor is a counter puncher and his style isn’t one to attack. He baits his opponent in and then unleashes a flurry of blows. There is no better example than in his UFC featherweight title fight on Dec. 12, 2015, against the legendary Jose Aldo.

McGregor infuriated Aldo during the lengthy build-up to the fight, which included a three-continent world tour. When the bell rang, Aldo charged at McGregor and fired a wild right hand. McGregor dodged it, cracked Aldo with a picture-perfect left cross and finished with a short hook.

Aldo was down and out.

In 13 seconds.

There is little chance, though, that Mayweather will charge McGregor. McGregor is going to have to lead and fight in a style that is not one he’s used to using.

But his best bet is to use his size and strength to muscle Mayweather to the ropes and then not give him any space to breathe. Jose Luis Castillo employed that tactic successfully in 2002. He’d pin Mayweather on the ropes for long stretches and did good work.

Mayweather won a controversial decision in their first bout – the closest he’s ever come to losing – but won the rematch. Marcos Maidana had some success with it as well in his first bout with Mayweather, though not as much as Castillo.

But both were vastly more experienced boxers than McGregor, who has never been in with anyone remotely as savvy as Mayweather.

“Everybody always says, ‘I have the remedy. I have the remedy. I have the remedy,’ ” Mayweather said. “The remedy is, come out there and do what you do. My job is just to go out there and be Floyd Mayweather.

“When we talk about IQ and wisdom in the sport of boxing, I’ve always had the best IQ. And with age comes wisdom, so I know what I can do when I face a guy who is throwing from different angles.”

McGregor also will likely go hard early, knowing it’s not likely he’ll be able to outbox Mayweather over 12 rounds. And if the gas tank gets low, he’ll face trouble because Mayweather is brilliant at walking his opponents into punches they don’t see.

If McGregor pulls it off, he’d instantly become the biggest figure in boxing and likely would call out the winner of the Sept. 16 middleweight title fight between Gennady Golovkin and Canelo Alvarez. He’d virtually be able to write his own paycheck.

It’s a tough task, though, to hit Mayweather cleanly just once, let alone a few times in a row, which it takes to drop the five-division champion.

McGregor will do everything humanly possible to win, but it’s not likely to be enough.

Expect Mayweather to cause swelling and open cuts around McGregor’s eyes, and stop it somewhere around the eighth round.

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