Anthony Yarde was knocked out by Sergey Kovalev after being unable to take advantage of earlier badly hurting the world champion.
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Yarde had been out-boxed by his vastly more experienced opponent in Russia but explosively unloaded in the eighth round and seemed to be just a punch away from a major upset victory.
But he couldn't stop Kovalev who recovered valiantly and ended his young challenger's chances in the 11th round by flooring him.
Yarde and his outspoken trainer Tunde Ajayi's decision to challenge for the WBO light-heavyweight title in the champion's hometown of Chelyabinsk after just 12 amateur fights and 18 unbeaten pro fights against a lower level of opposition had been derided as overly ambitious but his performance was hugely brave and nearly paid off.
His speed and punch power kept Kovalev honest but, as the fight wore on, Yarde was falling further and further behind on the scorecards. Kovalev's jab was his key.
Yarde's punch resistance, one of the biggest questions heading into his first world-title fight, was answered emphatically when he held firm against some of Kovalev's accurate punches.
The Londoner had never previously been beyond the seventh round of any fight and, at this stage on Saturday night, he seemed likely to slip to a decision loss.
But he emerged bullishly for the eighth round and hurt Kovalev to the body. Sensing an opportunity, Yarde flooded forwards and the champion was made to look uncomfortable, hurt and exhausted.
Kovalev staggered around the ring and Yarde swung for the knockout but failed to get the job finished.
The experienced champion recovered before the ninth and, with Yarde having gone for broke, Kovalev was able to navigate his way through the next few rounds.
Yarde was saved by the bell to the end of the 10th round when he was defenceless to Kovalev's punches with the referee considering stepping in.
But Kovalev landed a stiff jab, flooring Yarde, in the 11th and the fight was immediately waved off.
Kovalev, 36, could now be considered for a major fight against Saul 'Canelo' Alvarez.
Canelo had skipped his planned September 14 fight date to await the result of Kovalev vs Yarde and could be the next challenger to the Russian's WBO light-heavyweight title.
It would be a belt in a fourth weight class for Canelo, who currently holds middleweight world titles.
"This fight gives us an opportunity to fight with Canelo later on," Kovalev had said pre-fight.
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