NEW YORK — Defending champions Aryna Sabalenka and Carlos Alcaraz advanced to the U.S. Open quarterfinals Sunday with straight-set victories.

Sabalenka, the No. 1 seed, beat Taylor Townsend 6-4, 6-3. Townsend broke Sabalenka three times in her first four service games, but Sabalenka settled in and pulled away.

Sabalenka, who is seeking a three-peat at the U.S. Open, will face Wimbledon champion Linda Noskova, who beat Marta Kostyuk 7-5, 5-7, 6-4. She would be the first WTA Tour player to three-peat since Serena Williams in 2012-14.

“Probably they (people) don’t understand how hard it is mentally and physically to keep up the level and mentally stay kind of disconnected from that, because the moment you start thinking about that, you lose it,” said Sabalenka, referring to year-long pressure at the summit of sport. “They don’t understand how tough mentally it is constantly focusing on improving yourself.”

Alcaraz defeated Tommy Paul 6-4, 6-3, 6-4 to reach the quarterfinals for the fourth consecutive year.

The 23-year-old Spaniard has dropped just one set in four rounds and extended his Grand Slam winning streak to 18 matches. He is playing his first tournament since missing four months with a right wrist injury.

Charleston’s Emma Navarro, the No. 26 seed, faced No. 21 seed Anna Kalinskaya in the late match at Arthur Ashe Stadium on Sunday.

For the result of her match, find the story at postandcourier.com.

The winner will advance to the quarterfinals to face No. 3 seed Jessica Pegula, who had no trouble dispatching No. 16 seed Sorana Cirstea 6-3, 6-4.

Five American men reached the round of 16, the most at a Grand Slam since eight at the 1995 U.S. Open. Learner Tien, 20, is the youngest American man to reach the fourth round at the U.S. Open since Andy Roddick in 2002.

Frances Tiafoe beat seventh-seeded Daniil Medvedev 7-6 (1), 6-4, 7-6 (6), while Alex Michelsen defeated Tomas Martin Etcheverry 7-6 (6), 6-4, 6-4.