Kell Brook bravely stood toe-to-toe with middleweight king Gennady Golovkin before being pummeled to a fifth-round loss.
Gennady Golovkin retained his WBC and IBF middleweight titles after overcoming Kell Brook's stunningly daring high-wire act in five remarkable rounds at the O2 Arena.
Brook, who remains the IBF welterweight champion despite going down to a first career loss, stepped up two divisions to face the sport's most fearsome operator in Golovkin.
The 34-year-old Kazakh, now in possession of a remarkable record of 36 wins from 36 fights and 33 inside the distance, eventually stalked and pounded Brook to a standstill in round five as the Sheffield fighter's corner frantically waved a white towel.
Speaking after the fight, Brook said he believed Golovkin broke his eye socket during a barnstorming second round and his bloodied features told their own story when the end came after one minute and 57 seconds of the fifth.
Golovkin once again professed his desire to fight Mexican star Saul "Canelo" Alvarez and he remains on course for the superfight the sport desires above all others, although he did not have things all his own way in London.
Brook (36 wins, one defeat) entered the ring to his now customary theme song, Kanye West's 'All of the Lights', and received a rapturous reception.
He soon became aware of the grim task he faced when Golovkin got to work in the opening session, sinking in a trademark body shot and shuddering his foe with a left hook upstairs.
When a man facing Golovkin shows he is hurt, a procession normally follows but Brook recognised the need to fight fire with fire and a capacity crowd lapped it up.
Centre ring was the Sheffield favourite's sanctuary away from the ropes and he sent home a flurry of head shots off a lead right uppercut before the round ended.
Although the injury that would ultimately derail Brook came in round two, it was his most memorable of the fight as he scored frequently and showed himself to be Golovkin's equal in the clinches.
A right hook followed by a left uppercut landed flush. Golovkin absorbed them with little complaint as the volume in the arena cranked up a few more gears.
The pandemonium was punctured by gasps in round three as the champion landed rights with a sickening thud, with Brook coming back for more despite the right eye damage becoming apparent.
Alongside his freakish punching power, Golovkin's suffocating ring generalship is his greatest strength and, although Brook competed manfully in the fourth, the ring became an even more closed off and darker place for the brave Briton in the fifth.
The 30-year-old inexplicably beckoned Golovkin in to keep throwing punches, but his own artillery was no longer firing and trainer Dominic Ingle compassionately compelled referee Marlon Wright to halt the action.
Brook joined Golovkin in calling for a fight with Alvarez afterwards. He will have to get into line behind the sport's leading light, but thanks to Ingle's selfless act, his time to impress on the biggest stage will come again.