Image source, Reuters and Getty Images

So Sunday's final will be between two former champions, Juan Martin del Potro and Novak Djokovic.

Del Potro is through after Rafael Nadal retired when two sets down in their semi-final due to injury.

Djokovic has dispatched Kei Nishikori.

Read more on Del Potro's win here and Djokovic's win here.

This is what Nadal had to say about his future following his semi-final retirement.

That's all from us tonight. We'll be back at at 17:00 BST for the mixed doubles final featuring Jamie Murray and then it's the women's singles final between Serena Williams and Naomi Osaka at 21:00 BST.

See you then.

Djokovic on Sunday's opponent Juan Martin del Potro: "We have never faced each other in a Grand Slam final so that will be new for both of us.

"I have tremendous respect for him as a player and a person. He has come back from injury and is well respected in the locker room.

"He is a big match player and he showed that today against Nadal. I am sure it will be a thrilling match."

Djokovic is now sending the crowd wild by smashing the match balls into the stands.

One man dives full length onto the concrete steps to snatch the ball out of another spectator's hands...

Novak Djokovic in his post-match interview: "It felt great. I thought I came out of the blocks with great intensity and focus.

"Kei Nishikori is one of the quickest movers on the court. He takes away a lot of your time but I thought I took the points and played really well.

"The majors are the biggest events we have in tennis and obviously every player wants to perform their best in Grand Slams.

"I have lost some big finals but also won some. Every time I come back to Arthur Ashe stadium I relive these memories and they give me a lot of strength.

"It means the world to me. I am trying to be the best that I can be. I am working hard every day and I am trying to reach certain heights that I visualise every time I accomplish something big. I don't see any limits. I keep on going and hopefully you are enjoying my tennis."

Image source, Getty Images

Sunday will be Djokovic's 23rd Grand Slam final.

It'll be his eighth at Flushing Meadows.

He's going for a third title in New York and a 14th major overall.

Jill Craybas
Former world number 39 on BBC Radio 5 live sports extra

Djokovic was coming up with shots on the defence that were just unbelievable. He can turn points around so well. It eventually ground Nishikori down physically and mentally.

That lasted just two hours 22 minutes.

Djokovic has made Nishikori look like an easy opponent when in truth he was excellent in the second set.

Djokovic applauds as the Japanese player leaves the court.

Russell Fuller
BBC tennis correspondent on 5 live sports extra at Flushing Meadows

Boy does he look good! Juan Martin del Potro waits in Sunday's final.

Here's chance number two for Novak.

A huge cheer. A few cries of "come on Novak".

Now hush...

Into the net from Djokovic. We're not done quite yet.

Deuce.

Nishikori is putting up some final resistance. He gets to 30-30.

But Djokovic is too good tonight. He forces his opponent wider and wider.

Match point...

Thumping forehand from Djokovic. He saves one of his best for the end. 30-15.

Novak Djokovic will now serve for a place in the US Open final.

He loses the first point. 0-15.

Russell Fuller
BBC tennis correspondent on 5 live sports extra at Flushing Meadows

Djokovic has that cushion and what a cushion it is. It's very plump!

Novak Djokovic roars and punches the air. He knows he's almost there now. He has the double break. Nishikori looks like he could fall asleep in his chair. He rubs his forehand with thumb and forefinger.

Djokovic is casually sitting with one leg up on the other.

The end is nigh it seems. Everyone seems very distracted now, even Nishikori.

15-40. Two break points for Djokovic.

Nishikori may well be feeling the effects of the five-set marathon against Marin Cilic in the quarter-finals. He's two sets down here and Djokovic looks far, far fresher.

Nishikori doesn't even move after making a return out wide and as a result Djokovic can just chip the ball into the open court.

Ever the grumpy perfectionist Novak screams at his box after missing out on a break point. His wife Jelena isn't too concerned. She's giggling about something.

Nishikori takes the game to stay in touch but you wouldn't know it. It's a slow walk back to the chair.

Djokovic is sensing he can get back to the hotel in time for a movie.

Deuce.