Australian Danny Green produced a big shock by knocking out Roy Jones Jr in the first round of their IBO cruiserweight title fight in Sydney.
The 40-year-old Jones, who was seeking a ninth world title, was floored inside the first minute by a brutal punch.
Jones got up but Green continued the onslaught and the referee stopped the bout after two minutes, two seconds.
After only his sixth loss in 60 fights, Jones, who had eyed a bout with Bernard Hopkins, has hinted at retirement.
Jones Jr beat Hopkins to win his first world title in 1993 and floored Britain's Joe Calzaghe in the first round when the pair met for the Ring Magazine light heavyweight championship in New York in November 2008, before losing unanimously on points.
He has won eight world titles in four different weight divisions and has been referred to as the best pound-for-pound fighter in the world.
But he was felled for only the third time in his career and succumbed to the quickest defeat of a professional career that began way back in 1989.
Green, who only came out of a 13-month retirement in April, was close to apologetic after winning his 28th fight out of 31, 25 of them by knockout.
"That almost hurt me to do that to someone whom I aspire to look up to as a professional fighter inside and outside the ring," he said.
"I am just overwhelmed - this is the greatest victory in my entire life."
Jones Jr is now unlikely to continue in the ring and said: "I have got to take my hat off to Danny, it was a great performance. I guess now I go back into retirement."