Mayweather beats Japan's Nasukawa by technical knockout

Floyd Mayweather beat Japanese kickboxing phenomenon Tenshin Nasukawa by a technical knockout on Monday in the first round of a New Year's Eve "exhibition" bout that brought the US boxing superstar out of retirement.

Mayweather floored Nasukawa, a kickboxer less than half his age, three times in the first round of the three-round contest before the Japanese fighter's trainer rushed in to stop the fight.

The American boxer at first appeared not to be taking the fight seriously, grinning at his opponent and aiming only soft punches at him.

But he then demonstrated his power, launching a series of jabs and hooks to the head of the 20-year-old Japanese fighter, sending him to the canvas after just one minute.

Sensing his opponent was struggling, Mayweather stepped in for the kill, unleashing a flurry of punches that left Nasukawa reeling again within just two minutes of the bout and facing his second standing count.

With the Japanese fighter clearly struggling to stay on his feet, the trainer rushed in and stopped the fight with just one minute of the first round remaining.

The 41-year-old Mayweather carried a more than 4kg (9lb) weight advantage into the ring.

The rules were very strictly defined: three, three minute bouts and boxing only -- kickboxer Nasukawa was reportedly facing a USD5 million fine if he aimed a kick at Mayweather.

There were no judges, with only a knockout or technical knockout considered a victory in the bout, promoted as a pure exhibition match.

Crucially, the match did not feature on the record of either man, allowing them both to retain a cherished unbeaten record.