New York is known as the city that never sleeps – and so it has been at this year’s US Open.

A number of matches have started late and finished in the early hours, backing up the city’s reputation as a playground for the nocturnal.

But when some players – including men’s semi-finalists Ben Shelton and Alexander Zverev – are heading to bed as Manhattan commuters are waking up for work, it raises questions about fairness.

Three of top seed Zverev’s five matches over the past fortnight have finished past 1am.

“I’ve been to bed as late as 6:45am in the past week so I’m kind of a bit jet-lagged,” Zverev said.

“I feel like I’m playing the Australian Open in New York right now.”

Friday’s semi-final against Karen Khachanov – not before 15:00 local time/20:00 BST – will be the first time the German has played in the day at this year’s US Open.

By contrast, unseeded Khachanov has not been on court beyond midnight. He also has slightly longer to prepare after his quarter-final against Alexander Blockx finished shortly before 19:00 local time on Wednesday.

American eighth seed Shelton did not complete his last-eight victory over Carlos Alcaraz until 3:34am on Wednesday.

Shelton faces 11th seed Frances Tiafoe, who wrapped up his quarter-final about 19:00 on Tuesday after beating US compatriot Alex Michelsen in a five-set epic.

“The advantage of the opponent who has played earlier in the day will be big – they’ve had that full evening’s rest and a good night’s sleep,” Matt Little, who was Andy Murray’s long-time strength and conditioning coach, told BBC Sport.

“We can all relate to it – if you have one really bad night’s sleep, you have the knock-on effect of that for the coming days.”

Little saw the effects first hand when Murray infamously finished a match at 4am at the 2023 Australian Open, with the former world number one managing only three hours sleep before returning to Melbourne Park about 11am the following day.

Zverev did not go to bed until gone 5am following his opening three victories at Flushing Meadows and stayed up to watch Shelton beat Alcaraz on his night off.

Shelton, who meets Tiafoe in Friday’s night session (19:00 local time/00:00 BST, Sat), insisted he would pull up “all right” after two days off court.

“He’ll have to be napping to catch up some sleep,” said Little.

“On the nutritional side, he’ll be making sure he gets as many carbs and as much protein as he can in for that next match, and trying to get back to a bit of a routine.

“It’s about making sure you can optimise the hydration and get as much sleep as possible without completely going into a full slumber.”

Murray described the situation in Melbourne – where he beat Thanasi Kokkinakis in the second-latest finish in Grand Slam history – as a “farce”.

Few disagreed, and slight tweaks have been made in an attempt to limit matches finishing at the crack of dawn.

In response to Murray’s match, the Australian Open cut the number of day-session matches on the main courts from three to two to reduce the risk of night sessions being delayed.

In early 2024, the ATP and WTA created new rules which prevented tour matches – played over three sets and not five like the Slams – starting after 23:00. These rules, however, do not apply at the majors.

Last week, former world number one Venus Williams and her opponent Sofia Kenin began their first-round match at 12:13am – the latest start in US Open history.

It was one of three matches which finished post-2am in the first seven nights, with three others ending after 1am, while Shelton’s victory over Alcaraz was the latest finish in US Open history.

“Something has got to give,” said 18-time Grand Slam singles champion Martina Navratilova. “This is not OK and it is not normal.”

Some argue these occasions are the essence of the US Open – and a raucous sporting representation of the city which never sleeps.

The volume of early-morning matches has increased at Flushing Meadows this fortnight, although Tuesday’s play finishing at 3:34am on Wednesday was the product of unusual circumstances.

All three preceding quarter-finals on Arthur Ashe Stadium – Aryna Sabalenka beating Linda Noskova and Jessica Pegula overcoming Emma Navarro, with Tiafoe’s win sandwiched in the middle – went the full distance.

Data shows matches are becoming longer – so what is the solution?

Starting the US Open night sessions earlier is the most common proposal.

That is met by a resistance from television executives and the practicality of New York life, with many fans unlikely to arrive at Flushing Meadows much before 7pm.

There is a more extreme suggestion – cutting back on the best-of-five sets format at the Slams.

That idea gained further traction after Andrew Abdo – Tennis Australia’s recently-appointed chief executive – suggested the Australian Open could look to reduce men’s matches to three sets in the future.

Abdo’s comments provoked a backlash, with Tiafoe among those defending the traditional way.

“Do I love five-setters? Absolutely not,” Tiafoe said.

“But it’s tennis, man. I grew up watching so many incredible five-setters.

“Novak-Rafa, Federer-Rafa, epic five-setters that go on for hours and hours. That’s the history of the game.”