Carlos Alcaraz captured the ATP Masters 1000 title in Cincinnati on Monday after world No. 1 Jannik Sinner was forced to retire while trailing 0-5 in the opening set. The Italian, who called for the physio moments before stopping play, told officials he “tried but couldn’t go on,” with tournament staff attributing the withdrawal to illness amid on-court temperatures above 30 °C. The abrupt conclusion ends Sinner’s 26-match winning run on hard courts and his 10-match unbeaten streak at the Lindner Family Tennis Center, where he was defending champion. Alcaraz, ranked No. 2, adds a sixth trophy of the season and strengthens his bid to regain the top ranking at the upcoming US Open. Both men had advanced to the final without dropping a set. Sinner, celebrating his 24th birthday two days earlier, dismissed French qualifier Terence Atmane 7-6(4), 6-2 in the semi-finals, while Alcaraz overcame an ailing Alexander Zverev 6-4, 6-3. The Spaniard now leads the head-to-head series 9-5. Tournament doctors will monitor Sinner’s condition ahead of Flushing Meadows, which begins next week. Should Alcaraz claim the New York crown, he would reclaim the No. 1 ranking regardless of Sinner’s result, adding another layer of intrigue to a rivalry that has produced four finals in three months.