Irishman Kevin McBride scored a stunning upset victory over Mike Tyson on Saturday after the former world heavyweight champion quit on his stool before the seventh round of their non-title bout.

Following his third loss in four fights, the man who burst onto the heavyweight scene in such explosive style two decades ago declared that his career in the ring was over.

"This is it. I'm finished. It's just not in my heart," the 38-year-old Tyson told a post-fight news conference.

"I'm just not interested in fighting anymore."

Similar to his recent knockout defeats to Britons Lennox Lewis and Danny Williams, the end of the bout came swiftly and surprisingly.

After starting brightly, a clearly exhausted Tyson head-butted McBride in the first minute of the sixth round, delivering a nasty cut over the Irishman's left eye.

With blood gushing down his face, McBride continued to work inside, pushing the flagging Tyson to the canvas as the round ended.

Appearing unhurt but short of energy, Tyson staggered to his corner and slumped on his stool where his cornermen requested referee Joe Cortez to stop what could be his last fight.

"I can't do this anymore," said Tyson, who was dejected yet very calm at his news conference.

"I can't lie to myself. I'm not going to embarrass the sport."

At 6ft-6ins and weighing in at 271 pounds, McBride was seven inches taller and 38 pounds heavier than Tyson and the size advantage took its toll as the bout progressed.

McBride's record improved to 33-4-1 with 28 knockouts but Tyson is clearly the most impressive scalp on the Clones native's record.

RIGHT TIME

McBride, whom few people gave a chance heading into the fight, said Tyson is "still brilliant" as a fighter.

"He's a tough warrior," the 32-year-old McBride said. "He's perhaps one of the greatest warriors of all time. I just got him at the right time.

"This win was for the pride of Ireland," he added.

Tyson, still millions in debt after declaring bankruptcy, said he made the decision to retire before the fight if he lost, but would have continued had he won.

If this is to be his last fight, he retires with a 50-6 record that includes 44 knockouts. He will pick up $5 million (2.76 million pounds) for the fight while McBride's purse will be just $150,000.

Tyson did not display his usual aggressiveness in the early rounds but managed to score with sweeping hooks to the body and sharp uppercuts.

McBride, however, refused to buckle and began scoring as Tyson started to fade.

With Tyson gasping for air and becoming desperate, he appeared to try to snap McBride's arm coming out of clinch in the sixth round. Seconds later, he head-butted his Irish opponent.

Cortez deducted two points from Tyson although two judges still had the American 57-55 ahead at the end of six rounds while the third had McBride leading by the same margin.

"I don't know if it's the end of the road for Mike Tyson," McBride said. "But it sure is the start of the road for me."