Carlos Alcaraz, of Spain, serves to Matteo Arnaldi, of Italy

NEW YORK (AP) — Carlos Alcaraz had little trouble beating unseeded Matteo Arnaldi 6-3, 6-3, 6-4 on Monday to reach the U.S. Open quarterfinals, the third time in as many appearances he’s gotten at least that far at Flushing Meadows.

The No. 1-seeded Alcaraz, who is seeking to defend his title after winning Wimbledon in July, said afterward that he now prefers hard courts over any other surface and also likes playing under the Arthur Ashe Stadium roof. He enjoyed both against the 61st-ranked Arnaldi, an Italian who proved little match for Alcaraz’s power, which produced 31 winners.

By advancing to the round of eight, the 20-year-old Spaniard became the youngest player to reach three U.S. Open quarterfinals in the open era that dates to 1968 and the only player other than Andre Agassi to do so before turning 21.

Alcaraz next faces the winner of the night match on Ashe between sixth-seeded Jannik Sinner and No. 12-seeded Alexander Zverev.

In Louis Armstrong Stadium, eighth-seeded Andrey Rublev of Russia slugged his way past Jack Draper of Britain 6-3, 3-6, 6-3, 6-4 to advance to his fourth U.S. Open quarterfinals and the ninth Grand Slam quarterfinals of his career. He will await the winner of the match later between third-seeded Daniil Medvedev, the 2021 U.S. Open champion, and 13th-seeded Alex de Minaur.

Earlier, Madison Keys overpowered fellow American Jessica Pegula 6-1, 6-3 in just over an hour to book her spot in the quarterfinals.

Keys, the No. 17 seed and 2017 runner-up at Flushing Meadows, converted on 77% of her first-serve points and used powerful ground strokes to keep rallies short — a little over three strokes on average — to make quick work of her third-seeded opponent and close friend.

For Pegula, it marked yet another Grand Slam disappointment. She has advanced to the quarterfinals in each major tournament but has yet to reach the final four.

Keys’ quarterfinals opponent will be ninth-seeded Marketa Vondrousova of the Czech Republic, who came back to beat unseeded American Peyton Stearns 6-7 (3), 6-3, 6-2 to keep her dream alive of a second straight Grand Slam title after winning Wimbledon in July.

“I actually didn’t expect it after Wimby, there was a lot of pressure,” Vondrousova said in her postmatch interview. “Let’s see what happens next.”

Other fourth-round action on a Labor Day that saw both sunshine and sprinkles at Flushing Meadows includes Aryna Sabalenka, who will become the new No. 1 in the WTA rankings after the loss of top-seeded Iga Swiatek, against 13th-seeded Daria Kasatkina.