Top seed Alexander Zverev endured another gruelling five-set US Open match as he overcame Quentin Halys at 02:15 local time to reach the third round.

French Open champion Zverev is one of the favourites for the title, with world number one Jannik Sinner missing with injury and defending champion Carlos Alcaraz working his way back to fitness.

However, the German was taken to five sets in his first match and his level fluctuated wildly against world number 52 Halys on a humid evening in New York.

An exhausted Zverev raised his arms aloft after completing a 6-4 4-6 7-6 (7-3) 6-7 (3-7) 6-3 win in four hours and 33 minutes.

"I hope at some point I'll start playing better," Zverev said afterwards.

"It's great to be announced as the top seed on this court until you almost lose every time."

The 29-year-old is the first top seed in the Open era to play two five-set matches in the first two rounds of a major.

World number two Zverev faces another late night of recovery, having not gone to sleep until 5am on Wednesday morning after his victory over Lorenzo Sonego.

Zverev's side of the draw opened up even further on Thursday - but it remains to be seen if the Wimbledon runner-up has the form to take advantage.

Zverev is the only top-20 player remaining in his quarter of the draw and will face 25th seed Alejandro Tabilo - who he has never lost to - next.

Italy's Lorenzo Musetti, who has a winning 3-2 head-to-head over Zverev, was a potential fourth-round opponent.

However, the 13th seed is out after struggling physically in a 3-6 6-1 6-2 6-2 loss to Australian wildcard Dane Sweeny.

Based on seedings, Zverev could have faced sixth seed Alex de Minaur in the quarter-finals, but the Australian also lost on Thursday to Botic van de Zandschulp.

Six of the players left in the men's draw have reached Grand Slam singles finals - and only three have lifted a major trophy.

Zverev won this year's French Open and Alcaraz has seven major titles to his name, while Daniil Medvedev won the US Open in 2021.

Fifth seed Taylor Fritz, who lost just two games in his second-round win, was runner-up to Sinner in New York two years ago and is a potential semi-final opponent for Zverev.

French Open runner-up Flavio Cobolli was taken to five sets in his first round and needed four to see off qualifier Tristan Schoolkate in round two, while two-time major finalist Stefanos Tsitsipas has struggled for form in recent years.

Zverev could only meet second seed Alcaraz - his main pre-tournament rival for the title, despite the Spaniard having barely played for four months with a wrist injury - in the final.

Third seed Felix Auger-Aliassime is the highest-ranked player to exit in the men's singles draw so far in New York.

The Canadian, a two-time semi-finalist at the tournament, said he was "dizzy and seeing spots" in a surprise 6-7 (5-7) 6-3 6-2 6-2 to Karen Khachanov.

The 26-year-old said he had started to feel unwell early on against Khachanov.

"After a set and a half, I just couldn't feel well and was dizzy and seeing spots and couldn't recover," he said. "I thought maybe it would pass, but it didn't.

"I've never felt quite like that. I've had cramps before. I've felt tired towards the end of matches, but in a normal way.

"This was abnormal a little bit, and there were no signs in the last couple of days and no signs this morning, as well."

Gael Monfils' Grand Slam career came to an end with a 6-3 6-4 6-3 loss to 14th seed Learner Tien.

Frenchman Monfils, a crowd favourite wherever he played, is retiring at the end of the season.

Asked what his future plans were, Monfils said: "I already sign to work in wealth management in a Swiss company.

"So my next chapter is working in office and working in finance.

"I will always have a look on tennis, because I love the sport. My wife's playing."