Novak Djokovic set up a blockbuster US Open semi-final with Carlos Alcaraz after delivering a gritty performance to beat American Taylor Fritz.

Fourth seed Fritz applied constant pressure to Djokovic's serve, but the Serb fended off numerous break points and a hostile crowd en route to a 6-3 7-5 3-6 6-4 win.

Djokovic said he thought he was "lucky" at times, adding: "It was an incredibly close match, it was really anybody's match."

"I think for most of the second and third sets he was the better player."

Djokovic now must overcome second seed Alcaraz if he is to reach the final and continue his pursuit of a record 25th Grand Slam singles title.

The Spaniard - 16 years Djokovic's junior - earned his spot in the last four earlier on Tuesday when he raced to a 6-4 6-2 6-4 victory over Czech Jiri Lehecka.

The remaining men's singles quarter-finals take place in New York on Wednesday, eighth seed Alex de Minaur facing Canada's Felix Auger-Aliassime before world number one Jannik Sinner takes on fellow Italian Lorenzo Musetti.

Alcaraz, together with Sinner, has become a dominant force of men's tennis after the dominant era of Djokovic, Roger Federer and Rafael Nadal.

With Federer and Nadal both retired, Djokovic is the only active member remaining from the iconic trio, and time is not on his side as he chases the 25th major that would take him clear of Australia's Margaret Court.

But against Fritz, he showcased some of the resilience that has often defined his outstanding career.

Djokovic got off to a fast start as he broke Fritz's opening service game on the way to a 3-0 lead, and - after missing a set point at 5-2 - the Serb fended off a Fritz fightback, saving five break points before eventually serving out the opener.

Fritz continued to threaten in the second set, but he grew increasingly frustrated as he squandered opportunities before Djokovic pounced to go 4-3 up.

But, just as Djokovic was serving for a two-set lead, the Californian finally converted his first break point - at the 11th time of asking.

However, he dropped three double faults and an unforced error in the next game, and Djokovic then made no mistake in closing out the set.

The atmosphere became somewhat hostile in the third set, when Djokovic complained to the umpire about spectators shouting out during his serve.

Sensing his irritation, some of the crowd started jeering the four-time winner, while their cheers for home hope Fritz grew even louder as the 27-year-old took advantage of the disruption to break for a 4-1 lead.

Djokovic regained his composure to work his way through the fourth set, and he struck the decisive blow at 5-4, with a double fault from Fritz sealing his place in the last four after a gruelling three hours and 24 minutes.

"That last game was nerve-wracking, honestly tough one for Taylor to finish with a double fault; he didn't deserve that," Djokovic added.

"In many of my service games, I was just trying to stay alive, fight for every ball.

"In this kind of match, key points decide the winner."

'I'm here to entertain' - Alcaraz

Alcaraz has defeated Djokovic in two Wimbledon finals, but Djokovic has been triumphant in their last two meetings - including at last summer's Olympic final.

The five-time Grand Slam winner said he is "here to entertain" after his brilliant 6-4 6-2 6-4 display against Lehecka.

He displayed a laser-like focus throughout the match, but also found time for some showmanship during the victory as he thrilled the crowd with his astonishing repertoire of shot-making.

"Sometimes I play a shot that I should not play in that moment but it's the way I love playing tennis," Alcaraz, 22, told Sky Sports.

"I want to play solid, play well and play smart but at the same time when I have the opportunity to play a great shot - or a hot shot, let's say - why not?

"I'm here to entertain the people, myself and the team."

It is the third time Alcaraz, who won the US Open in 2022, has reached the semi-finals in New York.

He has reached the last four of a Grand Slam without dropping a set for the first time in his career - and is the youngest man to do so since Rafael Nadal at the 2008 French Open.