Kell Brook put in a valiant display but surrendered his IBF welterweight title following an 11th-round stoppage defeat to Errol Spence Jr at Bramall Lane.
Fighting in front of around 27,000 highly-partisan fans in his home city of Sheffield, Brook more than matched Spence Jr for the first eight rounds but swelling over his left eye ultimately turned the bout in the American's favour.
Brook rallied from a 10th-round knockdown but, with his left eye nearly closing, he took a knee in the 11th and referee Howard Foster opted to end the contest.
It later transpired Brook had suffered another fractured eye socket wound - similar to what happened in the Gennady Golovkin fight last September.
It was only the second defeat of Brook's 38-fight professional career, while Spence significantly enhanced his reputation as he improved his record to a perfect 22-0, with 19 of those wins coming inside the distance.
The Star boxing panel thought Brook was trailing in the fight on their score card - and with the Sheffielder already having had serious surgery to his other eye after losing to Golovkin, he did the right thing.
It had been a lifelong dream to fight at Bramall Lane - but his health has to come first.
Spence Jr is rated "the real deal" by no lesser an authority than Sugar Ray Leonard and the 27-year-old lived up to the billing as his speed over Brook's power eventually told.
Brook was making the fourth defence of his world title but was fighting for the first time since suffering his maiden loss in the paid ranks when he stepped up two weight classes to challenge middleweight king Gennady Golovkin last September.
The 31-year-old sustained a broken right eye socket in the fifth-round stoppage loss which required surgery to repair and there were fears the injury, as well as coming back down to the 147lb division, could significantly hinder him, with even his promoter revealing he would have preferred his charge to campaign at light-middleweight.
But he opted to remain at welterweight and take on his mandatory challenger Spence Jr, who reached the quarter-finals at the London 2012 Olympics and came highly-rated from his fellow Americans, including Leonard and former pound-for-pound king Floyd Mayweather.
He did not seem remotely fazed by the occasion as he made the step up to world level for the first time after a successful first four years as a professional - despite being vociferously booed on his way to the ring.
The Texan landed a telling body blow early on but it was Brook who was enjoying the better of the exchanges in a largely cagey opening round before bringing the crowd to their feet with a flashy right hand and uppercut.
He was on the defensive in the next as Spence enjoyed his best round with more body blows although Brook did nail his foe with another crisp right hand.
Spence Jr, rated the favourite by bookmakers, was bleeding from his mouth at the start of the fourth but was starting to come into his own in a bout that was increasingly becoming a tactical battle.
The American was sent into the ropes and looked momentarily unsteady following an overhand right from Brook in the fifth, but the younger man came back strongly with a ferocious body attack that seemed to unsettle his opponent.
A couple of tight rounds ensued but Spence Jr's rapier punches seemed to be taking their toll as Brook's left eye started swelling rapidly.
Brook was left hanging on at the end of the ninth as the tide turned firmly in Spence Jr's favour, the challenger bombarding the champion with a flurry of blows.
Brook was down in the 10th after Spence Jr continued the assault but the Briton, roused by a boisterous home support, came roaring back and responded in kind.
But Brook, nursing the opposite eye that needed surgery, was down again, voluntarily taking a knee. It proved to be the final action as Spence Jr claimed a ninth stoppage win in a row and, most importantly, Brook's world title.