Quick start to the third from Nishikori. Djokovic doesn't look too interested in it to be honest.
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Djokovic 6-3 6-4 0-0 Nishikori*
Here we go again. Good luck, Kei. You've got work to do.
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Djokovic 6-3 6-4 0-0 Nishikori
Novak Djokovic has nipped off court. Nishikori is up jumping around on the spot to try and keep warm.
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David Law
BBC Radio 5 live sports extra commentator at Flushing Meadows
If Djokovic carries on like this, he will take some stopping.
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Jill Craybas
Former world number 39 on BBC Radio 5 live sports extra
Djokovic likes to feed off the fans. He loves that energy!
Game and second set - Djokovic
Djokovic 6-3 6-4 Nishikori
There's the emotion from Novak Djokovic! He bellows and waves his arms after sealing the set. He just needs one more set to seal a place in a second successive Grand Slam semi-final.
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*Djokovic 6-3 5-4 Nishikori
A hum goes around Arthur Ashe Stadium. A roar of encouragement.
Two set points...
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*Djokovic 6-3 5-4 Nishikori
Novak Djokovic, serving for a two-set lead...
Big serve. 15-0.
Nishikori goes wide. 30-0.
Nishikori has to to fight and fight just for a point. He manages it. 30-15.
Post update
David Law
BBC Radio 5 live sports extra commentator at Flushing Meadows
Novak Djokovic looks totally in control. He has no doubts about what he is going to do.
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*Djokovic 6-3 5-4 Nishikori
Nishikori puffs his cheeks, lifts his shirt up onto his shoulders and takes a seat. He's forced Novak Djokovic to serve it out.
Now Nishikori wraps himself in his towel, closes his eyes and devours one of those energy gels. Can it lift him?
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Djokovic 6-3 5-3 Nishikori*
Nishikori is dragging his feet along the baseline between points. He whacks his heel with his racquet after netting.
You've got to feel for him.
15-30.
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Djokovic 6-3 5-3 Nishikori*
The all-action Nishikori is looking pretty sweaty again. He's swinging from the hip, like he has to, but those shots are just missing now. He used an awful lot of energy at the start of this set. Can he keep going?
Djokovic moves to within a game of a 2-0 lead.
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*Djokovic 6-3 4-3 Nishikori
Gasps from the crowd. Novak Djokovic made an error. Tonight that's remarkable.
The Serb looks to be feeling like Superman right now. He's already wandering towards the service line before Nishikori has even hit his serve and then taking the ball on the rise.
The return is powerful but just long. Nishikori stays in touch.
Post update
David Law
BBC Radio 5 live sports extra commentator at Flushing Meadows
Nishikori must wonder what else he can do? I feel a bit sorry for him. He is trying his heart out and at times is playing as well as he can play. Listen to that applause. They know he is trying.
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Matthew Henry and Emma Sanders
All times stated are UK
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Post update
Jill Craybas
Former world number 39 on BBC Radio 5 live sports extra
He does look a little bit defeated now Nishikori. He gave everything in that second set.
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Djokovic 6-3 6-4 3-1 Nishikori*
The pain of this situation is clear on the face of Nishikori now. He looks a beaten man. Djokovic is just strutting around smashing serves.
Djokovic waves a clenched fist in celebration and skips on his toes, proving to his opponent that he'd be happy to go the distance if he had to.
Djokovic breaks
*Djokovic 6-3 6-4 2-1 Nishikori
He's almost there!
Kei Nishikori is running out of gas. He makes another error.
Djokovic calmly wanders to his chair and takes a seat with his chest puffed out. This has been good. Very good.
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Djokovic 6-3 6-4 1-1 Nishikori*
Big danger for Nishikori now. This could be terminal. He nets and covers his face in his towel.
Two break points Djokovic.
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Djokovic 6-3 6-4 1-1 Nishikori*
Ah. Nishikori knows he's not going to get many chances like this. He sinks into a crouched position after netting a return.
Djokovic holds.
Post update
*Djokovic 6-3 6-4 0-1 Nishikori
The crowd needs a shot or a point from Nishikori to latch on to. This all looks to be going one way and as a result things have got a little subdued.
Nishikori is still looking busy, bobbing around at the back of the court.
Maybe Djokovic hasn't quite fully reengaged. 30-30.
Post update
*Djokovic 6-3 6-4 0-1 Nishikori
Quick start to the third from Nishikori. Djokovic doesn't look too interested in it to be honest.
Post update
Djokovic 6-3 6-4 0-0 Nishikori*
Here we go again. Good luck, Kei. You've got work to do.
Post update
Djokovic 6-3 6-4 0-0 Nishikori
Novak Djokovic has nipped off court. Nishikori is up jumping around on the spot to try and keep warm.
Post update
David Law
BBC Radio 5 live sports extra commentator at Flushing Meadows
If Djokovic carries on like this, he will take some stopping.
Post update
Jill Craybas
Former world number 39 on BBC Radio 5 live sports extra
Djokovic likes to feed off the fans. He loves that energy!
Game and second set - Djokovic
Djokovic 6-3 6-4 Nishikori
There's the emotion from Novak Djokovic! He bellows and waves his arms after sealing the set. He just needs one more set to seal a place in a second successive Grand Slam semi-final.
Post update
*Djokovic 6-3 5-4 Nishikori
A hum goes around Arthur Ashe Stadium. A roar of encouragement.
Two set points...
Post update
*Djokovic 6-3 5-4 Nishikori
Novak Djokovic, serving for a two-set lead...
Big serve. 15-0.
Nishikori goes wide. 30-0.
Nishikori has to to fight and fight just for a point. He manages it. 30-15.
Post update
David Law
BBC Radio 5 live sports extra commentator at Flushing Meadows
Novak Djokovic looks totally in control. He has no doubts about what he is going to do.
Post update
*Djokovic 6-3 5-4 Nishikori
Nishikori puffs his cheeks, lifts his shirt up onto his shoulders and takes a seat. He's forced Novak Djokovic to serve it out.
Now Nishikori wraps himself in his towel, closes his eyes and devours one of those energy gels. Can it lift him?
Post update
Djokovic 6-3 5-3 Nishikori*
Nishikori is dragging his feet along the baseline between points. He whacks his heel with his racquet after netting.
You've got to feel for him.
15-30.
Post update
Djokovic 6-3 5-3 Nishikori*
The all-action Nishikori is looking pretty sweaty again. He's swinging from the hip, like he has to, but those shots are just missing now. He used an awful lot of energy at the start of this set. Can he keep going?
Djokovic moves to within a game of a 2-0 lead.
Post update
*Djokovic 6-3 4-3 Nishikori
Gasps from the crowd. Novak Djokovic made an error. Tonight that's remarkable.
The Serb looks to be feeling like Superman right now. He's already wandering towards the service line before Nishikori has even hit his serve and then taking the ball on the rise.
The return is powerful but just long. Nishikori stays in touch.
Post update
David Law
BBC Radio 5 live sports extra commentator at Flushing Meadows
Nishikori must wonder what else he can do? I feel a bit sorry for him. He is trying his heart out and at times is playing as well as he can play. Listen to that applause. They know he is trying.