New York, Sep 8 (IANS): Spanish teenager Carlos Alcaraz has said that the two high-intensity four-hour five-setters took their toll on his body because of which he was forced to retire from the quarterfinal match against Canada's Felix Auger-Aliassime.

Auger-Aliassime made his first major semifinal at the US Open after Spanish giant-killer Alcaraz retired due to an undisclosed injury 6-3, 3-1 at the Flushing Meadows.

Alcaraz had made history at this US Open, becoming the tournament's youngest men's quarterfinalist in the Open Era. But the 18-year-old had to retire on Tuesday evening during the second set of his match due to a right adductor injury.

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

Alcaraz battled hard against Auger-Aliassime, but coming into the match off back-to-back five-setters against Stefanos Tsitsipas and Peter Gojowczyk did not help the Spaniard's cause.

"To play two matches [that went to] fifth sets in a row, play on a great level, in a great intensity [for] four hours, it was really tough for me," Alcaraz said.

"I am not used to playing these kind of matches in a row. I think it was really tough to recover [for] the next matches."

One year ago, Alcaraz was outside the Top 200 of the ATP rankings. The teen began this event at world No. 55, and his performance showed that he remains on the way up. Alcaraz stunned third seed Tsitsipas in a third-round thriller and proved he is a threat on the world's biggest stages against the best players.

"These matches gave me a lot of experience, so I think this tournament made me mature a lot. I think I played great tennis for me," Alcaraz said. "I'm really happy to play a first quarterfinal in a Grand Slam. I think this tournament's going to be a great experience for me for the next tournaments."