Floyd Mayweather Jr defeated Conor McGregor with a 10th-round stoppage on Saturday to win their money-spinning superfight and clinch his 50th straight career victory.

The former welterweight boxing champion, who had emerged from a two-year retirement to take on the Irish mixed martial arts star, took his time to get going before dominating from the fourth round.

The end came with a tired McGregor doubled over on the ropes as Mayweather landed two hard left hooks, prompting referee Robert Byrd to intervene and declare a technical knockout.

The fight had followed a largely expected script but McGregor, in his first ever boxing appearance, by no means embarrassed himself.

Mayweather will now head into what he says is a permanent retirement with a perfect 50-0 record, one better than heavyweight legend Rocky Marciano.

Mayweather is also expected to be around US$200 million (S$272 million) wealthier, taking his career earnings to around US$1 billion.

McGregor, who was an unemployed former plumber four years ago before emerging as one of the biggest stars of the Ultimate Fighting Championship, is expected to earn around $100 million.