Tony Bellew's shot at becoming the first Briton to hold four world titles in a weight division ended in failure as Oleksandr Usyk produced a stunning finish in the eighth round at Manchester Arena.
The Ukrainian, initially cautious and behind on the cards, found rhythm around the midway point and, after following a jab with a brutal left hook, he was already smiling as Bellew tried to get back to his feet, to no avail.
Usyk's IBF, WBO, WBA and WBC world cruiserweight titles were safe, despite Bellew's solid counter-punching early on, when the undefeated and undisputed champion struggled with the Briton's movement.
Referee Terry O'Connor waved the bout off and while 35-year-old Bellew appeared dazed in the moments after, he quickly stated he had given "everything" he had.
It was a conclusive finish, befitting of a much-hyped champion, who is now expected to chase the glamour names of the heavyweight division.
"He is just so hard and so awkward. He is big and he overpowers you. I tried my best and he is probably the best cruiserweight that ever lived," Bellew told BBC Radio 5 live.
"It is heartbreaking because I gave it everything I had. Heavyweights stay away, he takes a great shot and I don't even know if I hurt him."
Bellew confirmed it would be his last fight, saying: "I have been doing this for 20 years, and it is over."
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Brutal end for Bellew
In what was just the sixth bout in men's boxing history where all four world titles were on the line, 31-year-old Usyk briefly appeared frozen but the pedigree which took him to Olympic gold at London 2012 shone through.
All week he cut a figure at ease, a man so confident in his sublime skill-set. Against Bellew, he simply would not be drawn into a brawl which could level the playing field. There was no room for the chance attached to a slugfest.
He was tentative early on in a bear-pit atmosphere. Through four minutes the champion barely threw a punch. After landing a solid counter-right, Bellew beat down on his shorts with both hands as if to urge his rival to attack.
As he was in the early stages of his first encounter with David Haye, Bellew was comfortable with his back to the ropes, pulling his right hand to counter repeatedly.
Usyk - just 16 fights into his career - was being forced to think about every move, though he landed a stinging left hook to the middle of Bellew's face in the fourth, forcing the Briton on to the back foot.
It was tense. The world's first four-weight world champion Tommy Hearns sat two rows from the ring. Enthralled like the masses, his eyes were wide as Usyk started letting his hands go by halfway.
His caution ebbed away, each shot that landed added belief and, with Bellew suddenly breathing more heavily in the eighth, Usyk threw shots which served to create space for the hook, sending Bellew down and into the ropes.
The fairytale career the Liverpool fighter has enjoyed was brutally ended but he had taken on a challenge few believed he could overcome.
One step too far on a remarkable journey
Bookmakers had made Usyk as short as 1-7 to defeat a man known for upsetting the odds.
Boxing simply to impress his father as a child, Bellew's mother said he would be "too soft" in this most vicious of sports.
And yet the Evertonian rose from the canvas to land the WBC cruiserweight title at his beloved Goodison Park in 2016, upset David Haye twice at heavyweight and somehow found himself starring in a Rocky movie.
But to topple a man as refined between the ropes as Usyk, Bellew would need every ounce of the ring craft acquired over his previous 33 outings.
Few in the sport study like he does, lending hope he would deliver on his words and "find a way" to fell a "monster".
Nine minutes in he appeared in with a shout, beating a mover at his own game by gallantly taking up a position on the ropes, often pivoting right before throwing the right hand.
The early rounds seemed to go his way but suddenly the sheer pressure that comes with concentrating against one so dangerous took its toll.
A three-time British amateur champion, and a British, Commonwealth and world champion as a professional, the Bellew journey in the ring is over. What a journey it has been.
For Usyk, the most exciting part of his own career looks set to unfold.
Analysis - 'Bellew went out on his shield'
BBC Radio 5 live boxing analyst Steve Bunce
That was the best opening three rounds of Tony Bellew's career. He made Usyk look ordinary. Then through the third and fourth rounds, something special began to happen. That was absolutely sensational finishing from Usyk.
Former WBC super-middleweight champion Richie Woodhall on Radio 5 live
Bellew will be heartbroken because you are when you lose a world title fight, but he couldn't have done any more. He gave everything and tactically he got it spot on, but he just couldn't maintain it. He can be proud of his career and his performance but he was beaten by an exceptional boxer.
I think to sum him up, Tony Bellew has been a true world champion who has come from nothing. He has been a tremendous advert for British boxing and he went out on his shield against an undisputed champion.
Reaction - 'Usyk will be a force at heavyweight'
Former two-weight world champion Carl Frampton: "Usyk kept his discipline after falling behind in the first few rounds. Constantly on the front foot and the pressure worked. Absolute credit to Tony on tonight and what he's done in his career. Commiserations Tony Bellew and congratulations Oleksandr Usyk. Great fight!"
Tyson Fury's former trainer Peter Fury: "This guy is going to be a force in the heavyweights also."
Commonwealth heavyweight champion Joe Joyce: "I thought it was a valiant effort and I have great respect that Tony Bellew took on the best and can retire knowing that he put 100% into his career!"