NEW YORK: Spanish teen Carlos Alcaraz, the youngest US Open quarter-finalist in 58 years, was forced to retire from his match Tuesday at the US Open with a right adductor injury.

Canada's Felix Auger-Aliassime led 6-3, 3-1 when 18-year-old Alcaraz retired from the match, sending his 21-year-old rival into his first Slam semi-final aganst Russian second seed Daniil Medvedev.

"It's really tough to end a great tournament like this," Alcaraz said. "I had no choice to still play. I have to take care of my body and to stay healthy. I didn't feel good to still play."

World number 55 Alcaraz, who ousted third-ranked Stefanos Tsitsipas of Greece in the third round, could have become the youngest US Open men's semi-finalist since 1960 and the youngest in any Slam since 17-year-old Michael Chang won the 1989 French Open.

He also would have been the first man to reach the US Open semi-finals in his debut since Eric Sturgess in 1948.

The right thigh issue came after back-to-back five-set matches.

"Before match I felt it," he said. "I start the match controlling the pain. In the beginning of the second set it started to (increase), the pain."

Alcaraz was the youngest US Open quarter-finalist since 1963 and made his deepest slam run.

"These matches gave me a lot of experience. This tournament meant to me a lot," Alcaraz said. "I played great. I'm really happy to play the quarter-final. This tournament is a great spring for me into other tournaments."

Auger-Aliassime and Alcaraz had the youngest combined ages of any US Open quarter-final or later match since Australian Pat Cash (19) met Sweden's Mats Wilander (20) in a 1984 quarter-final.

"It's unfortunate," 12th seed Auger-Aliassime said. "What he has done here hasn't been done in the Open era. He should be proud of himself with head held high."