Danny Williams saw his bid for the WBC heavyweight title end in a painful eighth-round loss to Vitali Klitschko.
The Briton was out-boxed from the start in Las Vegas, taking a nine-count in the first round, but showed phenomenal heart to fight on.
Williams fell to the canvas three more times and suffered nasty cuts as Klitschko picked him off with the jab.
And the referee wisely stopped the contest after the fourth knockdown, as Williams wobbled gamely to his feet.
The British challenger had weighed in at a record 19st 4lb for the fight and looked ponderous throughout.
But what he lacked in speed, Williams made up for in bravery as he withstood a series of loaded punches from the 6ft 7in Ukrainian.
Klitschko dispelled any doubts about his pedigree in a weak heavyweight division with a composed and classy display.
Aware that the challenger would try to make his bulk pay early on, he answered the onrushing Williams head-on and sent him spiralling to the canvas.
Williams barely made the count and was subsequently saved by the bell, but he went down again in the third round.
The 31-year-old rallied briefly in the seventh, giving his vocal fans the slenderest of hopes that he might yet stage one of the biggest comebacks in boxing history.
But Klitschko replied with another monster punch and secured the stoppage in the following round.
Afterwards, the Ukrainian - nicknamed "Iron Fist" - dubbed Williams "Iron Chin" for his resilience.
"It was amazing. I threw so many punches, but he has a big heart," said Klitschko.
"He has a lot of respect from me. I was surprised how strong his chin was and I am very happy and proud to defend my prestigious title for the first time.
"I feel this was the best performance of my career," he added, dedicating victory to democracy in Ukraine.
A despondent Williams paid his respects to the champion.
"He was a lot more awkward than I anticipated and was very clever, coming in and out on angles," he said.
"He didn't hit as hard as Mike Tyson but he was more consistent with his punches.
"The thought of the world heavyweight title kept me going, but he was just too good."
Williams was taken to a local hospital for a precautionary brain scan after the fight, while Klitschko also went to have X-Rays taken of his swollen hands.