Floyd Mayweather reminds fans that the fight will end in a knockout of Conor McGregor and that he won't listen to the critics. (0:28)

LAS VEGAS -- Floyd Mayweather's reputation is as one of the greatest defensive fighters of all time. As the highest-paid fighter in history, he has grossed nearly $1 billion in large part because of his "Money" persona and the skills to back it up.

So it may come to a surprise to some that Mayweather -- giving his best Joe Namath Super Bowl III proclamation -- is guaranteeing he will knock out Conor McGregor, the UFC star crossing over to boxing for a huge money fight when they meet on Saturday (Showtime PPV, 9 p.m. ET) at the T-Mobile Arena.

"One hundred percent, it will not go the distance," Mayweather told ESPN on Wednesday. "One hundred percent chance this fight won't go the distance."

Mayweather's greatest skill is on defense, where he is supremely difficult to hit with a clean punch. And while he often makes his opponents pay by landing his own assortment of shots, one thing he is not is a knockout artist.

In fact, Mayweather has not knocked out an opponent since his somewhat controversial fourth-round stoppage of Victor Ortiz in September 2011. In that fight, Mayweather reclaimed a welterweight world title when he nailed Ortiz -- after Ortiz dropped his hands and was looking at the referee, who had broken them from a clinch.

Prior to that KO, Mayweather's previous stoppage -- a no-doubt-about-it one with no controversy -- came when he blasted Ricky Hatton in the 11th round of a 2007 welterweight world title defense.

In all, Mayweather (49-0, 26 KOs) has stopped two opponents in his past 11 bouts.

And when he said Saturday's fight against McGregor wouldn't go the distance, Mayweather did not mean it would be because McGregor would somehow knock him out and score perhaps the biggest upset in sports history.

Mayweather, a supreme counterpuncher, said he will be aggressive and go forward even though McGregor's trainer, John Kavanagh, has said he was skeptical.

Asked why anyone should believe him based on his history, Mayweather was nearly indignant.

"We'll see. We'll see. At the end of the day you will see the results," Mayweather said. "This fight won't go the distance. Remember that, no matter what his coach say. His coach can't fight for him. When it comes down to it, it comes down to the two fighters. I just said what I said [about winning by knockout]. This is how I feel.

"I say I guarantee it won't go the distance. He says it's not going the distance. I say it's not going the distance. So it's obvious we going to come out from the opening bell and drop bombs."

Floyd Mayweather knocked out Ricky Hatton in the 11th round of a 2007 bout to defend his welterweight world title. GABRIEL BOUYS/AFP/Getty Images

Mayweather, 40, of Las Vegas, has rarely predicted he would score a knockout. He said the reason he's doing so for this fight with McGregor (0-0) is he will return to retirement and wants to make his finale memorable.

He also said he wanted to make up for the 2015 megafight with Manny Pacquiao that so badly disappointed.

"I'm doing this for myself and my family, but I want to give everyone a great show," Mayweather said. "Everyone deserves a good show. The Pacquiao fight wasn't exciting enough. That was on Pacquiao, but I have to give the fans a great show this time."

McGregor has predicted a knockout from even before the fight was made official. He initially predicted he would stop Mayweather in the fourth round. Then, after the Nevada State Athletic Commission agreed to grant a one-fight waiver to reduce the size of the gloves from the standard 10 ounces for junior middleweight fights to 8 ounces, which are for fights under 147 pounds, a thrilled McGregor predicted he would stop Mayweather inside two rounds.

"Floyd can talk about whatever he wants to talk about. He can talk any kind of trash he wants, because he's talking to the new God of boxing," Ireland's McGregor, 29, said. "If people are overlooking my size, power and youth, they shouldn't be. I'm very confident in those attributes. I believe I'll knock him out early.

"If you look at the way I fight, I am a fast starter. I come out and bang people right away. With 8-ounce gloves, I don't see him lasting more than one or two rounds."