Top seed Jannik Sinner won with relative ease but second-seeded Alexander Zverev needed six match points to finally advance into the ATP Montreal Masters quarterfinals on Saturday.
The leading pair at the US Open tune-up grappled with swirling winds that made ball control difficult as organisers raced to get the event back on schedule after a Friday rain washout.
Sinner posted a 6-4, 6-3 victory over Canadian-born Chilean Alejandro Tabilo, advancing in 80 minutes at the tournament, which ends on Monday due to Paris Olympic scheduling.
Zverev, the 2019 champion in Canada, overcame stiff late resistance from Dane Holger Rune, winning 6-3, 7-6 (7/5) with 21 winners including eight aces.
"With this wind, you won't be playing pretty tennis," Zverev said. "I had to find a way to win.
"I did that today – and we move on," said the player who leads the ATP with 49 match wins this season.
World No 1 Sinner improved to 24-1 this season on hardcourt.
The 22-year-old Italian became the first man since 2015 to reach the quarterfinals in his first 10 ATP tournaments of a year and has become the first qualifier for November's ATP Finals in Turin.
Sinner faced two matches on the day and next plays a quarterfinal against Andrey Rublev, a 6-2, 6-2 winner over Brandon Nakashima.
Rublev, seeded fifth, will compete in his ninth quarterfinal of the season.
He has now completed a career matched set of quarterfinal matches at all nine Masters 1000 tournaments.
Sinner said that while playing twice in a day is difficult, he could only look as far ahead as his first match.
"It felt like a good match but I knew I had to try and play one more time," Sinner said. "There's not much being happy afterwards... to recover is the most important thing.
"When you're a set and a break up, you want to try and win in straight sets. To get to the second match, you have to win the first one, even if it takes three or four hours."
Former US Open finalist Kei Nishikori extended his comeback story as he saved eight of 10 break points in a 6-3, 6-4 defeat of Portugal's Nuno Borges, last month's Bastad champion, for a last-eight spot.
Nishikori will try to reach his first ATP-level semifinal since 2021 in Washington later when he plays Italian Matteo Arnaldi, who advanced to the last eight 4-6, 7-6 (7/5), 3-0 when Alejandro Davidovich Fokina of Spain retired with stomach illness.
ZVEREV TO FACE KORDA
Delayed second-round matches were wrapped in early afternoon with recovering Hubert Hurkacz leading the way with his 4-6, 6-3, 7-6 (8/6) fightback win over qualifier Thanasi Kokkinakis, the fourth seed's first outing since knee surgery.
Poland's Hurkacz had not played since quitting injured in the Wimbledon second round and then heading home for a knee operation, with doctors telling him his season was over.
"I'm happy I'm able to compete and I wasn't that slow today," he said. "Since this was the first match since the surgery, it was a little bit unknown.
"I'm feeling quite decent. I spent a lot of last week in the gym."
Others into the third round were last week's Washington titleholder Sebastian Korda – a 6-4, 7-6 (7/4) winner over fellow American Taylor Fritz – and France's Arthur Rinderknech, who defeated Italian Flavio Cobolli 6-3, 6-2.
Korda then reached the quarters as sixth seed Casper Ruud was forced by illness to pull out of their third-round match, sending the American against Zverev.