Novak Djokovic outlasted Alexander Zverev, while Daniil Medvedev defeated Felix Auger-Aliassime, in the men's singles semifinals at the US Open on Friday.

Novak Djokovic is through to his ninth US Open final after a five set win over Alexander Zverev

In Sunday's final, Djokovic will play Russian second seed Daniil Medvedev

Victory for Djokovic would give him a record 21st major title and complete the calendar Grand Slam

Novak Djokovic has reached a record-breaking ninth US Open final, after a tricky five-set victory over Olympic champion Alexander Zverev.

After winning the Australian Open, French Open and Wimbledon this year, the Serbian has a shot at becoming the first man to win a calendar Grand Slam for 52 years after Rod Laver in 1969 and collect a record breaking 21st major title, giving him one more than his great rivals Rafael Nadal and Roger Federer.

Laver was watching on as Djokovic doggedly fought his way through this nearly four-hour match.

As in his previous three rounds, the Serbian had to come from a set down, but a clinical serving game and sloppy errors from his fourth-seed opponent saw him prevail in what was his toughest match of the tournament so far.

Djokovic, who has not played his best tennis in New York, but still found a way to win, suffered a break of serve late in the first set when he double-faulted while he was down 40-15. The rest of the set raced away from him and just by keeping things tight, Zverev had a 1-0 lead.

The German was on a 16-match win streak, including Olympic gold medal and Cincinnati title and had only lost one set all tournament before Friday. Djokovic had a match on his hands.

In the second set, he snapped back into action, upping the tempo and forcing Zverev to play loose and long shots. Zverev, who was attempting to become the first men’s player to reach back-to-back US Open finals since Djokovic in 2015 and 2016 was blown away. Djokovic was ruthless and relentless, breaking early and breaking again. 6-2 and the match was all square.

The third set was tight and contained some of the best points this tournament has seen. But it was mired with Zverev frustration, as fractional judgments on the ball tracking cameras went against him. At least three times, the German looked up at the big screen in disbelief as the little yellow dot clipped the thick white line. Djokovic was safe.

In what proved to be the final game of the set, Zverev found himself 40-0 down while on serve. He lost rallies of 18, 32 and 12 shots, but then out of nowhere, took on Djokovic at his own game and won rallies of 21 and...incredibly… 53 shots.

The longest rally of the tournament lasted well over a minute but ultimately could not stop Zverev from losing the game and the set. 2-1 Djokovic and one set from the final.

But he could not capitalise on the momentum. Zverev broke Djokovic in the fourth game and sailed through the rest of the fourth set, holding his serves while not really putting Djokovic under much pressure to be broken again.

In the decider, Zverev was on the back foot straight away, losing his first service game and finding himself 3-0 down.

He couldn’t make up for it. In fact, he only made things worse for himself. Needlessly loose shots followed and Zverev lost another service game. He looked at his coaching team for an answer, but by then it was too late. Djokovic held serve to make it 5-0, Zverev made it 5-1 and even managed to break Djokovic, to the delight of his fans.

But there would be no comeback. Djokovic shut the door to win 4-6, 6-2, 6-4, 4-6, 6-2.

Afterwards, he showed his appreciation to the boisterous crowd inside the Arthur Ashe stadium.

“Everyday you look for the motivation to do the same things over and over again but it all pays off in this incredible atmosphere,” he said.

When asked what he did when he was under pressure, Djokovic said: “You are by yourself. There is no escape so you have to find a way. There is no secret to success, it is just many things combined.

“Tennis is a beautiful sport, a very demanding sport and you have to have your mind and body balanced if you are to compete for the big titles.”

Djokovic, who already has three US Open titles to his name, will play world number two Daniil Medvedev on Sunday evening after the Russian beat Felix Auger-Aliassime in three sets.