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.
Post update
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."
Post update
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...
Post update
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."
Getty ImagesCopyright: Getty Images
Djokovic reaches US Open final
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.
Post update
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.
Djokovic reaches US Open final
Djokovic 6-3 6-4 6-2 Nishikori
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.
Post update
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.
Game, set and match - Djokovic
Djokovic 6-3 6-4 6-2 Nishikori
Serene!
Novak Djokovic is back in the US Open final.
Post update
*Djokovic 6-3 6-4 5-2 Nishikori
Here's chance number two for Novak.
A huge cheer. A few cries of "come on Novak".
Now hush...
Post update
*Djokovic 6-3 6-4 5-2 Nishikori
Into the net from Djokovic. We're not done quite yet.
Deuce.
Post update
*Djokovic 6-3 6-4 5-2 Nishikori
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...
Post update
*Djokovic 6-3 6-4 5-2 Nishikori
Thumping forehand from Djokovic. He saves one of his best for the end. 30-15.
Post update
*Djokovic 6-3 6-4 5-2 Nishikori
Novak Djokovic will now serve for a place in the US Open final.
He loses the first point. 0-15.
Post update
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!
Djokovic breaks
*Djokovic 6-3 6-4 5-2 Nishikori
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.
Post update
Djokovic 6-3 6-4 4-2 Nishikori*
The end is nigh it seems. Everyone seems very distracted now, even Nishikori.
15-40. Two break points for Djokovic.
Post update
Djokovic 6-3 6-4 4-2 Nishikori*
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.
Post update
*Djokovic 6-3 6-4 3-2 Nishikori
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.
Post update
Djokovic 6-3 6-4 3-1 Nishikori*
Djokovic is sensing he can get back to the hotel in time for a movie.
Live Reporting
Matthew Henry and Emma Sanders
All times stated are UK
Get involved
Reuters and Getty ImagesCopyright: Reuters and Getty Images 
Getty ImagesCopyright: Getty Images 
Latest PostPost update
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.
Post update
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."
Post update
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...
Post update
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."
Djokovic reaches US Open final
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.
Post update
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.
Djokovic reaches US Open final
Djokovic 6-3 6-4 6-2 Nishikori
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.
Post update
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.
Game, set and match - Djokovic
Djokovic 6-3 6-4 6-2 Nishikori
Serene!
Novak Djokovic is back in the US Open final.
Post update
*Djokovic 6-3 6-4 5-2 Nishikori
Here's chance number two for Novak.
A huge cheer. A few cries of "come on Novak".
Now hush...
Post update
*Djokovic 6-3 6-4 5-2 Nishikori
Into the net from Djokovic. We're not done quite yet.
Deuce.
Post update
*Djokovic 6-3 6-4 5-2 Nishikori
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...
Post update
*Djokovic 6-3 6-4 5-2 Nishikori
Thumping forehand from Djokovic. He saves one of his best for the end. 30-15.
Post update
*Djokovic 6-3 6-4 5-2 Nishikori
Novak Djokovic will now serve for a place in the US Open final.
He loses the first point. 0-15.
Post update
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!
Djokovic breaks
*Djokovic 6-3 6-4 5-2 Nishikori
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.
Post update
Djokovic 6-3 6-4 4-2 Nishikori*
The end is nigh it seems. Everyone seems very distracted now, even Nishikori.
15-40. Two break points for Djokovic.
Post update
Djokovic 6-3 6-4 4-2 Nishikori*
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.
Post update
*Djokovic 6-3 6-4 3-2 Nishikori
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.
Post update
Djokovic 6-3 6-4 3-1 Nishikori*
Djokovic is sensing he can get back to the hotel in time for a movie.
Deuce.