The most improbable fight, one between an all-time great in Floyd Mayweather and an opponent, Conor McGregor, making his boxing professional 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 Saturday night at the T-Mobile Arena.

PPV issues will delay the Floyd Mayweather-Conor McGregor main event Saturday night in Las Vegas, sources told ESPN's Sal Paolantonio.

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," Mayweather said.

There was no logical reason to give McGregor, a UFC champion and one of the best mixed martial artists in the world, a chance, 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 he said was part of his game plan.

McGregor was the one who dreamed up the fight, which has a chance to break all combat sports revenue records, when he mentioned his interest in leaving MMA for a fight with Mayweather during a television interview in 2015. Mayweather, happily in retirement, eventually came around and public ate it up.

After a slow start, Floyd Mayweather came on strong and finished McGregor at 1:05 of the 10th round. Mayweather said afterward that this was his final fight. Mark J. Rebilas/USA TODAY Sports

It had a delicious 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, he never stopped trying and he got in a few solid shots in the early going.

McGregor 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 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.

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 they 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 while 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 his 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 McGregor down and 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.

It was Mayweather's first knockout since he stopped Victor Ortiz in the fourth round of a welterweight title fight in 2011.

WATCH VIDEO