On the women’s side, reigning Grand Slam champions Elena Rybakina and Mirra Andreeva also booked third-round berths after late games, along with fourth-seeded Coco Gauff.
The men’s sixth-seed, Alex de Minaur, and 13th-seeded Lorenzo Musetti followed third seed Felix Auger-Aliassime in tumbling out of the competition.
Zverev laboured until 2.15am on Friday at the Arthur Ashe Stadium to shake off 52nd-ranked Frenchman Halys 6-4, 4-6, 7-6 (7/3), 6-7 (3/7), 6-3.
The four-hour 33-minute marathon followed his wild first-round five-setter against 89th-ranked Lorenzo Sonego that kept Zverev at it until shortly before 2am on Wednesday.
“I won, that’s the most important thing,” Zverev said afterwards.
“Physically, I feel fine. I am proud, I think, to be physically quite strong. I just hope at some point I’ll start playing better tennis.
“I’m winning ugly right now. It’s also a skill to win ugly and when you’re not playing great tennis. I think I’ve mastered that right now.”
De Minaur fell to Botic van de Zandschulp 6-4, 7-5, 6-2 while 123rd-ranked Australian Dane Sweeny shocked 13th seed Musetti 3-6, 6-1, 6-2, 6-2 to reach the third round of a major for the first time.
It’s not the first time Van de Zandschulp has sprung an upset at Flushing Meadows, where he shocked Carlos Alcaraz in the second round in 2024.
Australian Open winner Rybakina, the world number two who is closing in on Aryna Sabalenka’s number one ranking, saw off Spain’s Jessica Bouzas Maneiro 6-2, 6-4, while Andreeva rolled over Germany’s Eva Lys 6-0, 6-2.
Former Australian Open champion Madison Keys had a harder time of it, needing to save five match points to beat Anna Bondar 4-7, 6-4, 7-6 (10/5).
There was a bittersweet goodbye on Louis Armstrong Stadium, where 20-year-old American Learner Tien ended 40-year-old Gael Monfils’ Grand Slam career with a 6-3, 6-4, 6-3 victory.
“It’s been a long ride,” Monfils told an adoring New York crowd. “You are my second best crowd. Of course, it can’t top Paris, but you are up there!” (AFP)