McGuigan made his first defence against American Bernard Taylor, who was stopped in the ninth round, and then against Danilo Cabrera, who got knocked out in fourteen rounds. This proved to be a controversial stoppage: the fight was stopped after the challenger bent over to pick up his mouthpiece after losing it, a practice that is allowed in many countries but not in Ireland. Cabrera was not aware of this, and the fight was stopped. Although Cabrera's corner protested the outcome, McGuigan remained the winner by a knockout. For his next defence, he went to Las Vegas in June 1986, where he faced the relatively unknown Stevie Cruz from Texas in what proved a gruelling fifteen-round title bout under a blazing sun. McGuigan held a lead halfway through, but suffered dehydration because of the extreme heat and wilted near the end, being dropped in rounds ten and fifteen. He eventually lost a close decision and his world belt, which he was never to reclaim. After the fight, McGuigan required hospitalisation because of his dehydrated state.