Carlos Alcaraz’s stunning run at the U.S. Open came to a sudden and surprising end on Tuesday night when the 18-year-old from Spain retired from his quarterfinal match against Felix Auger-Aliassime of Canada midway through the second set.

Auger-Aliassime took the first set, 6-3, and was leading 3-1 in the second set when Alcaraz approached the umpire and informed him that he was retiring from the match with an injury.