Shane Mosley was stopped for the first time in his career against Australian Anthony Mundine in Sydney on Wednesday evening.
The American was unable to come out for the seventh round after suffering back spasms following an exciting fight, which saw both players have success with big punches.
The former rugby league player started the fight well and looked to have the opening two rounds of the bout in front of his home crowd.
However, the former three weight world champion bounced back in round three when his right hand had Mundine shaken.
The fourth round was arguably the most exciting of the contest as the two fighters stood toe-for-toe in the middle of the ring firing exchanges at each other.
Mundine, four years the younger of the two men, looked to have done enough to secure the next two rounds before the fight was called to a halt as Mosley had to accept defeat when his back injury proved too much for him to continue.
Backers of the Australian in the betting were paid out as the American suffered a TKO defeat for the very first time.
Mosely, who took part in his 56th career fight, picked up $1 million for his appearance in Australia and is likely to go back into retirement.
He made a successful comeback against Pablo Cesar Cano in May but his latest defeat may mark the end of the 42-year old inside the ring for good.
Following the win over Mosely, Mundine is hoping to have grabbed the attention of the United States and will be looking for his next fight to be in America.
He suffered defeat earlier this year in a big domestic fight against Daniel Geale in January. However, fans who bet on boxing should note that his latest win could put him back on track for a world title eliminator in 2014.