LAS VEGAS -- The most improbable fight, one between an all-time great in Floyd Mayweather and an opponent, Conor McGregor, making his professional boxing debut, ended in the most probable way.

It ended with a dominant Mayweather stopping an outclassed McGregor by TKO in the 10th round of their massively hyped junior middleweight fight on Saturday night before 14,623 -- well under capacity -- at T-Mobile Arena.

Mayweather, who moved his record to a historic 50-0 with 27 knockouts, said after the fight he would return to retirement.

"This was my last fight tonight. For sure," Mayweather said. "Tonight was my last fight. Tonight I chose the right dance partner to dance with. Conor you are a hell of a champion."

With the victory, Mayweather surpassed the hallowed 49-0 mark that great heavyweight champion Rocky Marciano retired with. It's not a boxing record, but it is revered. There are some who said that beating an opponent with no boxing experience was a disgraceful way to pass Marciano, but Mayweather made no apologies.

"A win is a win, no matter how you get it," said Mayweather, who said during the buildup that he would consider it a failure if he didn't score a knockout. "Rocky Marciano is a legend, and I look forward to going into the Hall of Fame one day."

There was no logical reason to give McGregor, the UFC's 155-pound champion and one of the best mixed martial artists in the world but not a boxer, a chance in a boxing ring, but that didn't stop legions from cheering for the underdog. But in the end it was Mayweather, a five-division world champion and the greatest fighter of his era, whose class shined through after a bit of a slow start, which he said was part of his game plan.

Floyd Mayweather started slow but came on strong before finishing Conor McGregor at 1:05 of the 10th round. Mayweather said afterward that this was his final fight. Mark J. Rebilas/USA TODAY Sports

McGregor (0-1) was the one who dreamed up the fight, which has a chance to break all the combat sports revenue records set by Mayweather-Manny Pacquiao in 2015, when he mentioned during a television interview he was interested in leaving MMA for a fight with Mayweather.

Mayweather, happy in retirement, eventually came around, and the public ate it up. He ended a two-year layoff to make a guaranteed $100 million but likely will make well in excess of $200 million, while McGregor was guaranteed $30 million and likely will earn more than $100 million for a fight that had an irresistible storyline: Could an MMA great cross over to the boxing ring and do the unimaginable?

He couldn't, though he also showed his involvement in the fight was not the joke many said it was. He came to fight, never stopped trying and showed bravery, and he got in a few solid shots in the early going to make things interesting.

"I think we gave the fans what they wanted to see," said Mayweather, who guaranteed before the fight that it would not go the distance. "I owed them for the Pacquiao fight. I had to come straight ahead and give the fans a show. That's what I gave them. He's a lot better than I thought he'd be. He's a tough competitor, but I was the better man tonight."

Punch stats Punches Mayweather McGregor Landed 170 111 Thrown 320 430 Percent 53% 26% -- Courtesy of CompuBox

McGregor gave Mayweather his due.

"He's composed, he's not that fast, he's not that powerful, but boy, is he composed in there," McGregor said. "I thought it was close, though, and I thought it was a bit of an early stoppage. I was just a little fatigued. He was just a lot more composed with his shots. I have to give it to him, that's what 50 pro fights will do for you."

McGregor, a 29-year-old southpaw from Ireland, tried to go after Mayweather in the opening round, but he looked uneasy, and Mayweather moved around to get a good look at him. McGregor landed a couple of shots and put his hands behind his back at one point in a slow-paced round.

The slow pace continued in the second round, but McGregor was moving forward and touching Mayweather, though referee Robert Byrd warned him for hitting behind the head.

Mayweather, 40, of Las Vegas, finally started to get going in the fourth round as he began to land right hands against McGregor, who seemed to begin tiring; his mouth was hanging open. Mayweather also began to target McGregor's body.

Mayweather said the plan he and his father and trainer, Floyd Mayweather Sr., devised was to start slowly.

"Our game plan was to take our time, go to him, let him shoot his shots early and then take him out down the stretch," Mayweather said. "We know in MMA he fights for 25 minutes. After 25 minutes, he started to slow down. I guaranteed to everybody that this wouldn't go the distance.

Floyd Mayweather scored his first knockout since 2011, when he stopped Victor Ortiz in the fourth round of their welterweight title fight. Christian Petersen/Getty Images

"I want to thank all the fans from Ireland and all the fans around the world for coming to see this event. I couldn't do any of this without the fans."

It was Mayweather's first knockout since he stopped Victor Ortiz in the fourth round of a welterweight title fight in 2011. McGregor said he was disappointed that Byrd stopped the fight when he did.

"I've been strangled on live TV and came back," McGregor said, referring to his submission loss and decision victory against Nate Diaz in 2016. "When you're in here in the squared circle, everything is different. Let the man put me down. That's fatigue, that's not damage. Where was the final two rounds? Let me walk back to my corner and compose myself."

In the sixth round, Mayweather began to land hard head shots that pushed McGregor back. His face was beginning to show redness from the punches, but the heavily pro-McGregor crowd was not deterred as it began to chant, "Conor! Conor!"

Mayweather landed a right hand in the seventh round that snapped McGregor's head straight back. He continued to land crisp punches, whereas the shots McGregor landed didn't appear to have much steam on them.

McGregor went straight at Mayweather to open the ninth round and had to be pulled off his back by Byrd. But the rest of the round was all Mayweather, who laid punishment on him with an assortment of clean right hands, one of which swiveled McGregor's head. Later in the round, Mayweather landed brutal combinations against an exhausted McGregor, who showed enormous heart but was outclassed.

In the 10th round, McGregor had nothing left. Mayweather landed a huge right hand that nearly knocked him down, and he then continued the assault, landing about a dozen unanswered punches. McGregor was barely on his feet, and Byrd jumped in and stopped the fight at 1 minute, 5 seconds.

At the time of the stoppage, Mayweather led 89-82, 89-81 and 87-83 on the judges' scorecards.

Mayweather landed 170 of 320 punches (53 percent), according to CompuBox statistics, and McGregor landed 111 of 430 (26 percent). McGregor's punch output dropped dramatically in the ninth and 10th rounds when he was getting hammered, but he acquitted himself well.

Perhaps it was his age or the long layoff, but Mayweather, known for his defensive brilliance, got hit a bit more than usual. Nine Mayweather opponents landed less than 100 punches in a 12-round fight -- including Pacquiao, who landed 81 -- but McGregor landed 111 in 10 rounds.

Mayweather, however, said he fought exactly as he had planned.

"Our game plan was to go straight ahead," Mayweather said. "I said numerous times that I wouldn't back down, and that's what I did."