Unlike against Andy Ruiz Jr where he was undone by one solid punch, a too one-paced and one-dimensional Joshua was on the back foot throughout against an opponent who showed the greater guile, aggression and adaptability of the pair’s 12 rounds.
Prior to the bout, Joshua had promised to show how much he’d improved as a fighter but, if anything, he took a step back from the manner in which he won back his WBA, IBF, WBO and IBO heavyweight belts back against Ruiz and then successfully defended against Kubrat Pulev.
It was predicted that Usyk’s best chance of winning the fight was for it to go the distance and yet the Ukrainian also looked the likelier to get the knockout punch as an exhausted Joshua slumped on the ropes in the dying seconds of the final round with his right eye beginning to shut.
It resulted in a unanimous decision for the 34-year-old in front of a stunned 66,267 fans inside Tottenham Hotspur Stadium in only his third heavyweight fight since making the step up from cruiserweight. In the process, he followed Evander Holyfield and David Haye in becoming only the third cruiserweight champion to become heavyweight champion of the world.
This was a fight that had looked unlikely to happen with Joshua having been set to fight Tyson Fury back in August before Fury was ordered by an arbitration hearing to fight Deontay Wilder for a third time.
The prospective riches from facing Fury have now vanished with Joshua having to rebuild his career for the second time in two years. This time, that rebuild looks particularly daunting and improbable.
The fight was seen as the biggest challenge for Joshua since first becoming heavyweight champion against another Ukrainian in Wladimir Klitschko.
Technically, Usyk was the best opponent since, albeit questionable at heavyweight with just two fights at the weight having stepped up from dominating at cruiserweight. Giving away three inches in height and four in reach as well as 19lbs in weight, it had looked a potentially tough ask.
And yet there was still that unknown quantity about Usyk at heavyweight, a standout fighter at amateur level, capped by gold at London 2012 like Joshua, and only the second southpaw Joshua had fought in the pro ranks, the other being Charles Martin.
There had been question marks about Joshua too with his weight – coming into the fight at just over 17 stone after shedding some bulk, as well as his ability to last the distance or match the speed of Usyk. In addition, there were queries about the smoothness of his camp with trainer Rob McCracken out in Tokyo for the Olympics until last month.
Those questions proved correct to be asked as Joshua looked out of sorts all night and never really got going. The opening four rounds belonged to Usyk, most notably round three when a heavy right by the Ukrainian sent Joshua hobbling back.
Joshua made his first real statement of the night in round five, the first he had clearly won, as he did the subsequent round, briefly leaving his opponent on the back foot.
But just as the partisan crowd inside Tottenham Hotspur Stadium were beginning to build the noise and Joshua switching the momentum, Usyk pulled out his best round of the night in round seven.
Another hefty left by the southpaw sent Joshua stumbling back once more in the seventh and, from there, Joshua was never able to recover his way back into the fight, trainer McCracken repeatedly telling his rattled fighter to relax.
Quite what lies in store for Joshua after another chastening night remains to be seen, though a rematch is now highly likely. Meanwhile, the prospect of Fury looks incredibly far away.