Canada's Gabriela Dabrowski and New Zealand's Erin Routliffe opened their U.S. Open women's doubles title defence Thursday with a 6-4, 6-2 win over Canada's Leylah Fernandez and Yulia Putintseva of Kazakhstan.

Fernandez, from Laval, Que., and Putintseva broke serve on their first opportunity but their top-seeded opponents took the next four games en route to victory in 71 minutes.

Dabrowski, from Ottawa, and Routliffe will play American Catherine Harrison and Poland's Alicja Rosolska in the second round.

Dabrowski won mixed doubles bronze at the Paris Olympics earlier this month with Montreal's Felix Auger-Aliassime.

In men's singles, Montreal qualifier Gabriel Diallo upset 24th-seeded Arthur Fils of France 7-5, 6-7 (3), 6-4, 6-4 later Thursday in second-round play.

After winning the second set, the 20-year-old Fils went up 3-2 in the third before Diallo won four consecutive games to take the set. The 143rd-ranked Diallo did the same in the fourth set to win the match, which lasted three hours 29 minutes.

Diallo, 22, is set to face 14th-seeded Tommy Paul of the United States in the third round.

WATCH | Diallo through to 3rd round:

Canadian qualifier Diallo advances to 3rd round of U.S. Open with another upset win

After earning his first ever Grand Slam win on Tuesday, Montreal's Gabriel Diallo defeats 24th seed Arthur Fils of France 7-5, 6-7 (3), 6-4, 6-4 in the second round of the U.S. Open.

Alcaraz's Grand Slam win streak ends

Carlos Alcaraz's 15-match Grand Slam unbeaten run ended at the U.S. Open with a sloppy 6-1, 7-5, 6-4 loss to 74th-ranked Botic van de Zandschulp in the second round on Thursday night, a stunning result that eliminated the pre-tournament favourite.

This one was hard to predict, given Alcaraz's standing in the game, his excellence of late and his opponent's far-lesser resume.

Alcaraz won the French Open in June and Wimbledon in July to raise his career total to four major championships, including taking the title at Flushing Meadows in 2022.

But he never found his footing against van de Zandschulp, a 28-year-old from the Netherlands. Alcaraz was way off, repeatedly missing the sorts of shots he usually makes routinely. After double-faulting to fall behind two sets to none — a deficit he's never overcome — the No. 3-seeded Alcaraz slung his equipment bag over this shoulder and trudged toward the locker room.

Glancing in the direction of his coach, 2003 French Open champion Juan Carlos Ferrero, Alcaraz pointed his right index finger at his temple, then wagged that finger, as if to say, "I'm not thinking straight."

Sinner, Swiatek advance

Jannik Sinner and Iga Swiatek flashed their No. 1 form on Thursday with powerful performances that moved them into the third round of the U.S. Open.

Sinner downed Alex Michelsen 6-4, 6-0, 6-2 in one hour 39 minutes.

Later, Swiatek raced by Japanese qualifier Ena Shibahara 6-0, 6-1, winning the first set in just 23 minutes and finishing off the match in 65. It took the 2022 U.S. Open champion longer than that to play the second set alone in her first-round match, when she needed a tiebreaker that she eventually closed out in 72 minutes.

"I just felt the rhythm was much better," Swiatek said. "I was a bit tense in my last match, so today I just wanted to focus on the right things."

Rybakina withdraws

Sinner beat Michelsen for the second time this month, having also won a second-round match in Cincinnati shortly before it was revealed he tested positive twice for an anabolic steroid in March.

Another Italian, Jasmine Paolini, played just three points before advancing when Karolina Pliskova appeared to injure her left foot. The No. 5-seeded Paolini, who reached the finals of the French Open and Wimbledon in her breakout season, advanced past the second round of the U.S. Open for the first time.

"Finally, we made third round!" she said with a laugh during an interview on the court.

Paolini will next play No. 30 seed Yulia Putintseva.

No. 4 seed Elena Rybakina, the 2022 Wimbledon champion, withdrew from the tournament with an undisclosed injury before her second-round match, sending French qualifier Jessika Ponchet to the weekend.

"Unfortunately, I have to withdraw from my match today due to my injuries," Rybakina said in a statement. "I did not want to finish the last Grand Slam of the year this way, but I have to listen to my body, and I hope I can close out the remainder of the year strong."

No. 7 seed Hurbert Hurkacz was eliminated in straight sets by Jordan Thompson, and No. 16 Sebastian Korda was knocked out by Tomas Machac.

Osaka eliminated

Seemingly back in her U.S. Open match, suddenly a point from getting to a third set, Naomi Osaka lost her way Thursday night, missing forehand after forehand until she ceded that game and chucked her racket, sending it clattering on the Arthur Ashe Stadium court.

Not much later, she was out of the tournament, eliminated 6-3, 7-6 (5) by Karolina Muchova in the second round of an event where Osaka won two of her four Grand Slam titles.

Osaka — once ranked No. 1 but now No. 88 after missing nearly 1-½ years because of mental health breaks and time off to have a baby — struggled for much of the early going, dropping five consecutive games and 22 of 26 points in one stretch.

But she played much better in the second set, getting her only break of the evening to lead 5-4 and yelling "Come on!" when 2023 French Open runner-up Muchova netted a forehand. The crowd roared for Osaka.

Serving for that set, Osaka hit a 119 mph ace, her fastest of the match, to lead 40-love. That gave her three chances to extend the match to a third set. That's when Osaka really faltered, making five forehand errors, with a double-fault mixed in, to get broken.

When they got to the tiebreaker, it was Muchova who asserted herself, then used some scrambling defence on the last point, flinging the ball back over the net and seeing Osaka send a swinging volley out.