LAS VEGAS — Floyd Mayweather Jr. figured out a 50th opponent, letting Conor McGregor have the early rounds before stalking him late and leaving the mixed martial artist defenseless and exhausted on the ropes.

Mayweather battered McGregor around the ring in the later rounds, finally stopping him at 1:05 of the 10th round last night with a flurry of punches that forced referee Robert Byrd to stop the fight.

Before a pro-McGregor crowd that roared every time the UFC star landed a punch, Mayweather methodically broke him down after a slow start to score his first real stoppage in nearly a decade. He did it in what he said would be his final fight, against a fighter who had never been in a professional boxing match.

McGregor boxed surprisingly well early. But after landing some shots in the first three rounds, his punches seemed to lose their steam, and Mayweather went on the pursuit. McGregor backpedaled most of the way, stopping only to throw an occasional flurry as Mayweather wore him down.

“I think we gave the fans what they wanted to see,” Mayweather said. “I owed them for the [Manny] Pacquiao fight.”

McGregor had vowed to knock Mayweather out within two rounds, and he won the early rounds with movement and punches to the head. But the tide of the fight turned in the fourth round as Mayweather seemed to figure out what he had to do and began aggressively stalking McGregor.

McGregor turned in a respectable performance for someone in his first fight. But Mayweather’s experience and ring savvy paid off as he executed his game plan to perfection.

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“Our game plan was to take our time, go to him and take him out in the end,” Mayweather said. “I guaranteed everybody this fight wouldn’t go the distance.”

Mayweather was widely criticized for not going after Pacquiao in their megafight, and he didn’t make the same mistake this time. In a fight that could make him $200 million, he seemed to stagger McGregor with a series of punches in the ninth round, then came back in the 10th eager to finish it off.

McGregor went over and hugged Mayweather. He seemed almost happy in the ring afterward, secure that he had given a good performance even in losing.

“I was a little fatigued,” he said. “He was composed in there, that’s what 50 pro fights can give you.”

Mayweather ran his record to 50-0, surpassing Rocky Marciano’s 49-0 record and giving himself a great parting gift. He repeated afterward that he was not going to fight again.

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“This is my last fight for sure; 50-0 sounds good, I’m looking forward to going into the Hall of Fame,” Mayweather said. “I picked the best dance partner to do it with.”

Irish fans arrived by the thousands in the days before the fight, filling the arena for the weigh-in and boisterously cheering for their man. They even went off in the middle of the night and spray painted an Irish flag and “49-1” on a billboard on Interstate 15 promoting Mayweather’s businesses.

The capacity crowd at the arena cheered McGregor on, but they quieted as the fight progressed and Mayweather showed his dominance.

Cotto tops Kamegai. Miguel Cotto withstood constant early pressure from Yoshihiro Kamegai and picked up a pace as the fight wore on to take a unanimous decision for the vacant WBO junior middleweight title last night at sold-out StubHub Center in Carson, California.

Cotto (41-5, 33 KOs) won the sixth world title in his career, receiving winning scores of 120-108, 119-109 and 118-110 from the judges.

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In the postfight interview with HBO, Cotto, 36, said he wants to fight one more time in December.