Brook sunk to his knees with his swollen left eye causing obvious distress, and referee Howard Foster called a halt to confirm Spence Jr as the new IBF welterweight champion.Sheffield’s Brook had previously suffered a broken orbital bone in his middleweight defeat to Gennady Golovkin last September, but his other eye resulted in his demise against Spence Jr who was ahead on all three judges’ scorecards at the conclusion.The American challenger, a cool and composed character throughout the week despite being in enemy territory, began to quietly find a home for his trademark body shots from the opening bell.Brook’s counter left – a successful shot on multiple occasions, delivered over Spence Jr’s jab – was evidence that the Sheffield fighter retained his speed and reflexes upon his return to welterweight.Brook tried to bulldoze through his younger and less experienced foe, and sure enough, his trainer Dominic Ingle assured “he’s beginning to drain” after four rounds of tit-for-tat action.The champion appeared comfortable opposing a southpaw, as he has been on many occasions before, but Spence Jr proved a slick operator who justified the considerable hype generated from America. His punches to the body were never obvious but always present.Spence Jr needed to grit his teeth and persevere through a difficult sixth round when Brook turned up the heat, but the tables quickly turned.Straight left hands from the southpaw stance began to find Brook and, in the seventh, his left eye showed clear markings. The wound worsened swiftly.Brook needed the solace of the bell to the end of the ninth round as Spence Jr realised the IBF belt was within his grasp.Brook was then on the floor – a combination with a crunching punch to the mid-section from Spence Jr caused him to double-up in pain. His eye, by this point, looked appalling but he bravely roared on and, from the precipice of defeat, turned the round into a back-and-forth affair.But the injury was too severe and, with Spence Jr given an obvious target, it was causing more and more problems. Brook was blinking worryingly – an ominous reminder from his Golovkin fight – and he sunk to his knees before the referee saved him.