Alexei Popyrin insisted that his shock US Open triumph over defending champion Novak Djokovic was "not unbelievable" and that winning his maiden Masters title in Montreal on the eve of the tournament "was way bigger".

Novak Djokovic slumped to his earliest exit at the US Open in 18 years on Friday as a four-set, third round defeat to Alexei Popyrin sparked more questions over his long term future in the sport.

Djokovic, a four-time champion at the tournament and seeking a record 25th Grand Slam title, was leading 6-4, 6-4, 2-0 when Djere called it quits.

Midnight matches may be popular with fans but not with old campaigner Novak Djokovic, who bemoaned a late night at the start of his U.S. Open title defence on Monday.

Djokovic arrived on Arthur Ashe Stadium for his 40th career night match at the tournament with two gold bags slung over his shoulder in a nod to his recent Olympic success in Paris.

Djokovic, who will once again bid for a record 25th Grand Slam title at Flushing Meadows, has been upstaged by younger rivals this season, losing to Jannik Sinner in the Australian Open semi-finals and Carlos Alcaraz in the Wimbledon final.

Djokovic, speaking to reporters as he prepared to defend his US Open title, said players who have bemoaned a lack of transparency in the Sinner case make a valid point.

Jack Draper defeated Felix Auger-Aliassime at the US Open warm-up event on Friday despite a suspicion the ball hit the Briton's racquet and then the floor before it popped over the net to secure the match-winning point.

Following Novak Djokovic's dramatic gold medal victory at the Paris Olympics, Serbia is set to build a museum dedicated to the tennis great, according to the country's president.

Novak Djokovic described his Olympic gold medal triumph on Sunday as "probably" his "biggest sporting success" and revealed he may defend the title at the 2028 Los Angeles Games when he will be 41.

After heartbreak in Beijing, London, Rio de Janeiro and Tokyo, Djokovic simply would not be denied the one title that had eluded him for so long, winning 7-6(3) 7-6(2) in front of an enthralled crowd on Court Philippe Chatrier.

A fired-up Novak Djokovic on Friday reached his first Olympic Games final, where he will face Carlos Alcaraz in a dream gold medal showdown.

"I'm soaking wet, honestly," he said. "It's a very, very humid day as it was yesterday. I just hope it rains so it cools down the temperature a bit and the air," said Djokovic.

Rafael Nadal said he will make a decision on his future in tennis "after the Olympics" in the aftermath of a shattering straight-sets defeat to old rival Novak Djokovic at the Paris Games on Monday.

It was 24-time Grand Slam champion Djokovic's 31st win in a rivalry which began on the same Roland Garros clay courts in 2006.

Rafael Nadal and Novak Djokovic will do battle once more when they meet at the Paris Olympics on Monday while Australia's Ariarne Titmus is hotly tipped to win her second swimming gold of the Games.

Matthew Ebden had not expected to last long against Novak Djokovic in the first round of the Olympics on Saturday and he was not wrong - but it left the Serbian wondering why the Australian doubles specialist was competing in the singles.

The 38-year-old effectively ruled himself out of the singles tournament as he battles a thigh injury picked up in training at Roland Garros, the scene of 14 of his 22 Grand Slam triumphs.

Novak Djokovic lost just one game in his Olympic tennis opener on Saturday to set up a potential blockbuster clash against old rival Rafael Nadal.

Novak Djokovic says he has "high expectations" as he chases an elusive Olympic gold medal, with his confidence unshaken despite a poor year by his stellar standards.