Nishikori in unfamiliar territory - a first Grand Slam semi-final and facing a seven-time Grand Slam champion - but he comfortably negotiates the road blocks Djokovic tries to throw in his way. Another winner threaded down the line for a 40-15 lead. Djokovic overcooking a return. Nishikori a step closer to victory.

Image source, AP

A fourth double fault for Djokovic, who has only accumulated seven during the entire tournament. His serve wobbling and he's forced to watch Nishikori winners fly by. At 30-30 he's in choppy waters once again, but he manages to swim safely to shore. No arm bands or SOS flares required this time.

Michael Blighe:, external "I love Djoko, but Nishikori is doing a great job here. Hope he keeps it up!"

Lucy Foreman:, external "Great to see a good match and some more contenders for the open titles. Nishikori putting on a great show."

Shohidur Rahman:, external "Nishikori had to win that set coz of all the chances he had. Still backing Novak to come through in 5."

Image source, Reuters

Oohs from the crowd as Nishikori's forehand clips the net. It stays on course, but the 22-shot rally ends with the Japanese player going long. A tame netted backhand follows. Three break points Djokovic. Pendulum swinging at dizzying speed.

A powerful first serve from the 10th seed. 40-15. The Djokovic backhand faltering 40-30. One break point remaining... Nishikori sprinting towards the tape, Djokovic forced backwards with a deep volley... crisp overhead and he reduces the arrears. Djokovic returns lacking bite, Nishikori taking advantage. Sloppy from Djokovic. A vital hold for Nishikori.

Nishikori left the court after the third set, giving fans and players alike time to compose themselves. But Djokovic has yet to find his groove, coughing up a double fault to present his opponent with a double break point. Someone has turned off the lights. I'm not sure I can take anymore of this. A tired-looking forehand from the world number one and Nishikori has early advantage.

Piers Newbery
BBC Sport at Flushing Meadows

"On a sultry, stifling afternoon it's taken a while for Ashe to fill up and the atmosphere has been a bit woozy, but the man who has now been on court for over 15 hours this tournament has looked the liveliest out there, and the crowd are getting right behind him. Nishikori might have been based in Florida for many years but he is one set away from becoming very, very big news in Japan. Let's hope they're still up at 3:30am."

Pat Cash
1987 Wimbledon champion on BBC Radio 5 live

Image source, AP

"These are tough conditions. Really tough conditions. Extreme with the humidity. It is just hard to keep up the level all the time. Nishikori had to win that. I would be very surprised if he could outlast Djokovic over five sets and Djokovic knew that. It's amazing how the pressure turned around."

Back and forth the yellow ball goes... from side to side... hearts beating faster... 16 shots... 17 shots... Nishikori faltering on the 18th. 5-3 Nishikori.

The 10th seed still in command, but he double faults and, in a blink of an eye, his advantage is wiped away. 5-4 to the 10th seed with Djokovic serving. But, hang on, Djokovic directs a forehand into the tape, Nishikori with two set points.

And the world number one is gone gone gone! Nishikori a set away from victory! Djokovic crumbling like a chocolate flake, dragging a forehand wide. Will we go the distance?

Where were we? Ah, yes, Nishikori romping towards victory. Too much spin for Djokovic to handle and into the tape the Serb's forehand goes once more - 4-0 Nishikori! Could this be a whitewash? No. Let's not get carried away. Djokovic halves the deficit but he double faults! Oh, my giddy aunt. 5-2 Nishikori.

Russell Fuller
BBC tennis correspondent at Flushing Meadows

"Djokovic has not played with the fluency we expected and in the third set that has been down to Nishikori's attacking play."

Image source, AP

Nerveless from the 10th seed. First serve on target and he wins the first point. Djokovic's second serve punished and a gentleman in the crowd yells "yes" as the Serb falls 2-0 behind. Nishikori returning aggressively, Djokovic slapping a forehand into the tape. The underdog Nishikori leading 3-0.

Apparently it's a egg-frying 96 degrees on Ashe. I'm not sure what that is in new money. 35C perhaps? No sign of fatigue from Djokovic as he concludes a confident hold to love with an ace to the wings. Anyone for a tie-break?

Pat Cash
1987 Wimbledon champion on BBC Radio 5 live

"Nishikori's hitting the ball hard and fast - this is still a really tricky situation for Djokovic. If he does get this set you suspect Nishikori will have another dip, but if he doesn't then Nishikori will go for everything in the fourth set to try to get this over the line."

Image source, AP

Image source, AP

Hollywood actor Kevin Spacey is watching proceedings on Ashe. What does he make of the state of Nishikori's play? The 10th seed as ruthless as one of Spacey's characters, congressman Frank Underwood, collecting three easy points, and a screwed Djokovic return puts the 10th seed in front once more.

Two hours have elapsed since the start of this match and we're no closer to finding out who will win this ding-dong. From 40-15 to deuce and the crowd are whipped into a mini frenzy. A lung-busting baseline exchange... Djokovic slicing and dicing and his backhand forces Nishikori to net. Another boomer from the Serb outwits his opponent and the top seed gives out a full-throated roar, which can probably be heard in Staten Island.

Image source, Getty Images

Ben Roach:, external "That double fault could've cost Nishikori the match. Doubt Djokovic will allow that again!"

Image source, AP

Both players trading missiles from the baseline... Nishikori stepping forward, crunching a forehand winner to level at 15-15. A wince from Nishikori after the next point, he knows he should have done better than plonking his forehand into the tape. A mixture of brilliance and botched jobs from Nishikori. A dreamy backhand down the line for 30-30 but another unforced error presents Djokovic with a break point and the 10th seed surrenders meekly, a double fault. And Djokovic nods towards his camp as he confidently walks towards his chair.

Djokovic, an ice towel around his shoulders, focusing into the middle distance during the changeover, like a grand master planning his crowning move. Or maybe not. A double fault probably wasn't part of the grand plan. 0-15 Nishikori. Towards the net Djokovic goes and he does some damage, sending Nishikori haring down a blind alley before seeing him off with a canny volley.

Nishikori nibbles at Djokovic's lead, though, and at 30-30 the crowd sense danger for Djokovic. Wonderful retrieving from Nishikori! A fabulous crosscourt forehand for break point and Djokovic is beaten with a scintillating return.

Image source, Reuters

Pat Cash
1987 Wimbledon champion on BBC Radio 5 live

"Nishikori is doing well, he is not engaging in these long rallies. He knows he cannot match Djokovic in that department and that he is not going to win this match in five sets - four is his only chance."

Image source, Getty Images

A first ace of the match from Nishikori allows him to eke a 40-0 advantage and it's an impressive game from the 10th seed. A serve out wide... a thumping forehand to Djokovic's backhand side. A hold to love.