Be warned: Novak Djokovic has made a fool of those who have doubted him before.

Some questioned if the Serb would challenge for the sport’s top honours again after he dropped out of the world’s top 20 amid a two-year major title drought in 2018.

Djokovic proceeded to win four of the following five Grand Slams, doubling his tally of majors with 12 across the next six years.

But three years have now passed since he landed his men’s record 24th major title at the US Open.

And, as the 39-year-old fought back tears mid-match on Sunday night, this latest loss in New York felt different.

Staring at a first opening-round Grand Slam exit since 2006, one of sport’s all-time greats simply had nothing left, beaten 7-6 (7-5) 5-7 4-6 6-2 6-1 by Argentina’s Navone.

For so long now Djokovic has not only defied time, but appeared to be improving with it.

That was evident at this year’s Wimbledon, where he outlasted Felix Auger-Aliassime, 14 years his junior, in a five-set thriller that became the longest quarter-final in the tournament’s history.

Even in his late 30s, Djokovic has been the one challenging Jannik Sinner and Carlos Alcaraz, the new dominant forces in the men’s game.

At the Australian Open in January, he ended Sinner’s bid for a third-straight title in a sensational five-set comeback victory. He then led Alcaraz by a set in the final, before fading to a four-set defeat.

After early exits in Paris and New York, there is an inevitable sense that Melbourne was his best chance to secure an outright record 25th major triumph and cap a career unparalleled in every statistical measure.

Djokovic was despondent after the match, saying he “despised every moment I spent on the court for that”.

“When it comes to the match itself, and the overall feeling of how I felt with my body and playing, it was really not enjoyable,” Djokovic said.

“But, from the perspective of the crowd and support, it was incredible.

“I’m very sorry that I didn’t perform as well as I should have, could have, or wanted – for them.”

The four-time winner’s shock first-round US Open defeat means:

Djokovic’s refusal to disappear from contention on the sport’s biggest stages has prolonged the final embers of the ‘Big Three’ era that captivated crowds for the best part of two decades.

But, for the first time in almost 24 years, the next world ranking update will have a top 10 missing at least one of Djokovic, Rafael Nadal or Roger Federer.

Nadal, a 22-time major winner, called time on his career aged 38 in 2024, two years after 20-time slam champion Roger Federer did so aged 41.

While Djokovic, who will turn 40 next May, is still going, they all share one thing in common – they each last won a slam aged 36.

Ken Rosewall remains the oldest men’s singles slam champion in the Open era, winning the 1972 Australian Open two months after turning 37.

There is no doubt that the game has become far more physically demanding over the 54 years since.

Djokovic prevented Federer from breaking Rosewall’s record when he saved two championship points to win the 2019 Wimbledon final, one month before the Swiss turned 38.

And early exits are still rare for Djokovic at the Grand Slams. He has reached at least the semi-finals eight times at the past 12 majors.

Up until now, Djokovic has not been as physically hampered as Nadal and Federer were in their final years on tour.

But despite feeling that he had made his best recovery from a slam in two years post-Wimbledon, Djokovic recently revealed his struggles with an ongoing health condition that causes particular issues in hot, humid conditions.

Djokovic dropped to his hands and knees and required a medical timeout in a surprise second-round loss in such conditions at August’s Cincinnati Masters.

The New York humidity was largely irrelevant once the roof was closed after just seven games on Sunday night – but by then, Djokovic was already struggling.

He vomited and cramped during his four hours and 36 minutes on court, saying it felt as if his “whole body starts to collapse”.

Since winning his last slam, Djokovic achieved his lifelong goal of winning Olympic gold at Paris 2024.

With that triumph – two months after knee surgery and three weeks after losing to the Spaniard in the Wimbledon final – Djokovic became only the fifth player to complete the career ‘Golden Slam’.

Since then, his attention has been on breaking his tie with Margaret Court of 24 major singles titles.

He has slimmed down his schedule to prioritise the majors. In 2026 he has contested just seven tournaments – four Grand Slams and three Masters 1000 events – and his 21 Tour-level matches are his fewest in a season since 2004.

Reacting to Djokovic’s defeat, former Wimbledon champion Pat Cash said on BBC Radio 5 Live: “You can’t substitute matchplay. You can’t be walking into a Grand Slam on a hot and humid day and expect to get through a five-set match.

“I know he’s super-human in many ways but it’s going to catch up with you.”

Djokovic has stated his desire to continue in the sport until the next Olympics, in Los Angeles in 2028.

It would be a fitting stage for his farewell – not least that it would be exactly a decade since his ability to still compete for the biggest prizes was first questioned.

Discussing retirement in his recently released documentary, Djokovic said: ‘Why would I talk about retirement when I still keep proving to myself that I can still win?’

But, as of Sunday night, legitimate doubt has been cast on whether that remains true.