Anthony Joshua's reign as world heavyweight champion was ended and a 'Battle of Britain' against Tyson Fury is in tatters after Oleksandr Usyk claimed a stunning unanimous decision win at Tottenham Hotspur Stadium.
Usyk was giving up three inches in height and four in reach, as well as nearly 20lbs in weight, but the former undisputed world cruiserweight champion's technical acumen came to the fore in an electric atmosphere.
Joshua finished the bout slumped against the ropes as his smaller foe looked for a dramatic finish and while it was not forthcoming, Usyk claimed the WBA, IBF and WBO titles after he was given the nod by all three judges.
Scores of 117-112, 116-112 and 115-113 were just reward after a near-masterclass from the unbeaten Usyk, who became only the third fighter after Evander Holyfield and David Haye to win world titles at cruiserweight and heavyweight.
Joshua, who was obligated to face WBO mandatory challenger Usyk after a bout against Fury fell through earlier this year, seemed accepting of the result when the scores came as he suffered just the second defeat of his career.
He said on Twitter afterwards: "Keep positive even if the world's crumbling in front of you! London I love you & thank you each and every time!"
Anthony Joshua (R) in action against Ukraine's Oleksandr Usyk. Photo: Nick Potts/dpa.
As well as giving up several physical advantages to Joshua, Usyk had to contend with the hostile atmosphere that greeted his entrance to the ring from the 66,267 fans that attended this bout.
But he retained an intense focus throughout and his combination of speed and almost non-stop movement from an awkward southpaw stance befuddled Joshua, whose right eye became increasingly swollen as the fight wore on after a succession of rapid left hands found their mark.
Joshua was hurt on several occasions, most notably in the final seconds of the fight as a flurry of punches sent the Briton reeling back to the ropes, just about hanging on from the onslaught before being put out of his misery by the judges.
Usyk, who revealed earlier in the week his new-look shaven head and moustache was a nod to his Cossack ancestry, said via a translator on Sky Sports: "The fight went exactly as I expected it to go.
"There were a couple of moments when Anthony pushed me hard but nothing special. I had no objective to knock him out because my corner pushed me not to do that. At the start, I hit him and tried to knock him out but my trainer said 'just stop and do your job'."
The 34-year-old Ukrainian, who won Olympic heavyweight gold at London 2012 the day before Joshua memorably topped the podium in the super-heavyweight category, was slippery and threw in plenty of feints as his opponent tried without much success to establish his jab.
A pattern of success
This was just Usyk's third fight at heavyweight, having moved up to boxing's blue riband division two years ago, but he established an early pattern of success as Joshua was unable to get going and had his head jolted back in the third round by a picture-perfect left-cross before the outgoing champion fired back a warning shot.
But it was a fantastic start from the challenger, whose only concern early on was a small cut underneath his right eye, although Joshua got his right hand working in the fifth and sixth rounds, undoubtedly his best in the fight.
But Usyk reasserted his authority at the start of the second half of the fight, another left hook sending Joshua staggering backwards before regaining his footing.
Even at this point it seemed Joshua's grasp on his titles was slipping.
Another savage left in the ninth drew a nod of appreciation from Joshua, who had developed a welt under one of his eyes.
Both combatants seemed to slow down in the championship rounds but Usyk was still noticeably quicker than his foe.
Joshua entered the last round needing at least one or two knockdowns to have an impact on the scorecards but he could not fashion anything and it was Usyk who closed the show as the bell came to his opponent's rescue.