We have a John Isner tantrum. He taps his racquet on the floor.

Why? He's 0-30 up at 5-5 in the fourth and thinks Kyle Edmund has served wide. Isner cannot challenge, he's used his three. "That's so out," he shouts. Edmund is back to 30-30, he cares little for these emotions and closes the game out expertly. An ace followed by an Isner miscue.

Kyle Edmund with a super return, finding the feet of John Isner who just cannot respond. That's 15-30, Edmund is two points from the last-16.

Again there's an opening with Isner at the net, will Edmund make the pass? No, a very smart backhand volley creeps across court, 30-30. Isner's heart must have been in his mouth there. He's on the brink of exit.

He needs an ace... gets one... no. It's ruled out by hawkeye. Oh you can feel it's edgy. Gutsy as he responds by powering one down and Edmund can't clear the net.

Serve-volley from Isner, that's game and a big fist pump. We go on. We go on.

How many gorgeous sunset images can we get in this live text?

One more? Just look at it. It's like a scene from a Spielberg movie.

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Meanwhile, over on this beautifully crafted court, Rafa Nadal leads Andrey Kutznetsov 6-1 2-1.

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Kyle Edmund follows his opposite number to be 15-30 down on serve but a backhand from John Isner finds the net. He gives it the full monty, berating himself.

A nice rally breaks out, they move one another around a little, who will play their trump card? Isner rushes to the net, this will be key... brilliant backhand pass from Kyle Edmund. What a beauty, he steered that wonderfully and completes the hold on the next point.

Russell Fuller
BBC tennis correspondent in New York

I don't like watching ace after ace but when someone can do that three times in a row under intense pressure, you have to admire the skill required to do it.

I must admit, I thought John Isner was cooked. There's life in this yet though. Get a coffee in folks.

As this has evolved, it's not all about the serve. 

Yes, that terrible 43% of first serves in for John Isner in the third set was very costly, but across the four sets so far, the service stats are not too dissimilar. It's 64% of first serves in for Isner, 55% for Kyle Edmund.

The difference on the stats at least is in unforced errors, 40 for the American, 20 for the Briton.

A 900th ace of the season for Isner - just the 137mph - gives him game point having been 15-30 down and he closes it out, ace again - 4-4.

It's not about the serve, it's the errors.

When in doubt, when questions are being asked, when the pressure is on... go to what you know. 

Kyle Edmund resorts to default and that's the forehand. The first is a whipper down the line to earn a 40-30 lead, the second is across court and when he finally frees up his right hand it's to punch the air.

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Daniel Grinsted tweets us and goes for "nothing's working".

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A loose forehand from John Isner puts him 15-30 down on serve, there's a lob chance for Kyle Edmund here if he can make it to the bouncing ball near the net... it's six inches too long though as Isner turned around to stare at the dropping ball.

The American is using all his experience here, sending Edmund chasing on the next point and even an acrobatic slide can't retrieve that ball. Game point Isner... ace.

We were just saying the same thing Kurt. No sooner are we out of the late night trenches here we are back in them. Hang in there mate.

All credit to John Isner. His body language is that of a lost puppy between points but he's still slugging away when the ball is live.

At 30-30 in this Kyle Edmund service game he has hope but what a way to dampen it, a quite stunning cross-court backhand from Edmund. Even the stretch of the 6ft 10in American can't get there.

Edmund, sometimes called 'Kedders' by those he calls pals, closes out to lead 3-2.

We tick towards two hours of play as John Isner sends a kick serve down and Kyle Edmund finds the net. That's 40-30.

Isner has handed out 34 unforced errors so far to Edmund's 16. He holds though as the British player is long on another return.

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I'll go for: "I need my bed".

Some lovely disguise from Kyle Edmund as Jonh Isner runs to the net but the British youngster shapes to go across court but turns the wrist over nicely and wrong foots his man.

That's 30-15 and Isner again comes to the net. You get the feeling he's thinking it's time to throw all his chips on the table here. He seems more urgent. We arrive at deuce.

The American earns a break point as Edmund finds the net, saved though as the Edmund forehand shines through. Another stunner of a forehand gives Edmund game point and he clenches the fist as the game is confirmed. 

John Isner needs this lot badly.

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Kyle: Brilliant performance from Kyle Edmund and can see him winning the 4th 6-2. Isner has gone.

Daniel Grinsted: Come on Kyle one more set. Let's see that training with Murray paying off tonight. And I need to go bed soon!

Good stamina on show from you guys, hanging on in there. Who feels more tired, you or Isner?

You can see the belief coursing through Kyle Edmund now. At 40-30 he moves his body around a dropping ball and goes to his trusty forehand, fizzing it low over the net and it's good.

He flicks his wrist, shaking the racquet a few times in a show of conviction.