Courtney Nguyen
WTA reporter on BBC Radio 5 live sports extra

They probably aren't going to be out there long but it's such a huge mental stress to play John Isner.

There is a lot of taking on balls at shoulder height for Kyle Edmund. From a 6ft 10in frame and at an average of 124mph, those serves bounce. They bounce a lot.

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Here we go then, John Isner seeking parity and with the ball in his hand. 

With every toss of the ball into the air erupts a show of power and athleticism. He lands on his left leg which is strapped just above the knee. An ace brings up 40-0, just 115mph that one but well placed.

Three set points, ace on the second serve, 118mph. Blistering. We are level.

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Mike Dickson
Daily Mail tennis correspondent on BBC Radio 5 live sports extra

Edmund is getting a little bit outmuscled at the moment. Edmund hits it pretty hard but Isner is such a big presence. Isner is stepping up to the baseline and looking to dominate these rallies.

Kyle Edmund continues to look calm in the face despite the mounting pressure as a solid John Isner forehand takes this game to deuce.

With every serve Edmund's teeth become visible as he focuses on ball and target but there's a relaxed tone to his body language suddenly as a pulled backhand from his opposite number gives a second game point.

Again it slips away and suddenly Isner starts moving like a figure skater, gliding to meet an Edmund volley and whipping a ball across court. That's set point.

It's saved but Edmund concedes another with a wide passing attempt. Will John Isner convert this one? No. Ace. Isner looks to the sky, he wants to get it done here so he can serve first in the third set. No such luck, another ace. Game Edmund.

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John Isner a few feet from the net and in control as he slams one down the throat of Kyle Edmund who gets it back and forces a volley error. Still Isner has game point though and his second serve packs a lot of bounce, Edmund can only loop it long. We edge towards one set apiece.

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A second-serve ace from Kyle Edmund followed by a serve-smash combo. He glares at his opponent as if to emphasise some good work. 

Edmund's veins in his right bicep are visible, that's his serving arm and it's having to work very hard. John Isner is in conserve-energy mode, it's all about holding serve for him now.

A lot on the line as always. Just one Slam quarter-final in his 31 years on this earth. He'll want more before a few more years tick away.

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Much better as Kyle Edmund wins the fourth game of set two to love. He's reached 129mph with his own serve but the accuracy us beginning to wane a little, just 57% of first serves in compared to 75% from the American.

John Isner is now finding a rhythm on his serve so I'll keep it simple, three aces in a game to hold.

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Image source, Getty Images

Kyle Edmund was ranked as high as 191 at the start of 2015, he's now at 84.

"He's still going to get a lot more out of his serve as the years go on," said Great Britain Davis Cup captain Leon Smith. "His backhand has improved already a lot; his net game can keep getting better and of course he will get more robust physically."  

Twice Edmund has found himself in Miami for pre-season training - as a guest in Andy Murray's apartment - and carrying out the same hitting, fitness and weight training drills as the world number two. The top-10 and Grand Slam titles are a long way away but steps on the road to such glory have perhaps already been taken.

John Isner has hit 137mph on serve so far. He's just warming up.

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Some quality oozing from Louis Armstrong right now as John Isner serving floats a curling forehand around Kyle Edmund to level at 30-30. 

Edmund is having none of it and a two-hand backhand across court give him break point, great shot while on the run, great shot. Isner saves the break though, volley at the net with Edmund deep on the court, soft hands.

Deuce. Ace. Ace. Fist pump again.

It never looks all too comfortable when a big man tries a drop shot. It's like a hippo playing Jenga and with the court at his mercy, John Isner just flicks the ball into the top of the net to gift Kyle Edmund a way back to 30-30. Isner twirls his racquet on the floor, I think he's swearing in his head.

At deuce Edmund finds the net from behind the baseline and Isner has a break point, his first of the match. From deep he knows Edmund is at the net and he passes beautifully down the line. A smile, a big smile and a fist pump. At last he looks happy. Edmund will need to squash this quickly.

Russell Fuller
BBC tennis correspondent on BBC 5 live sports extra

"I do like the way Edmund is being so aggressive. Two or three times he's been under the high ball and he's hit it hard and deep."

Jonny Wan: Loving the calm and relaxed approach by Kyle. He is looking the real deal.

Do you fancy him to get this done Jonny?

CV: Thoroughly enjoying it :-) Heart saying Edmund in 3, head saying Edmund in 4.

Big caution there from your head CV.

Mike Dickson
Daily Mail tennis correspondent on BBC Radio 5 live sports extra

It's a little bit flat out there. It was a bit ugly in that last game but Edmund thoroughly deserves that first set. Isner played one shocking game where he couldn't get a first serve in and was broken to love and Edmund protected his serve from there on.

Kyle Edmund goes into this critical game having won 12 of 13 points on his first serve, make that 13 in 14. He's on point so far and has to be.

John Isner has made 10 unforced errors in nine games but there's one from Edmund as he finds the net and that's 15-15.

There are one or two in the crowd making some noise for their countryman and he manages a fist clench after forcing a mistake but a cracking serve to the body gives no wriggle room and Isner spoons a ball wide of the court, 30-30.

Two points needed, a 129mph serve equals ace all day long, set point. Edmund is too keen though, looping a ball long. You get the sense he knows this is massive. Isner puts his head in his giant hand after a tepid return, Edmund follows suit with a double fault. That's two set points gone, no one wants it.

A rally breaks out, Edmund always looks more comfortable when that's the case. He smashes emphatically across court from next to the net with Isner stranded and finally, he gets it right at set point, serving to the body and Isner is in a spider's web. Tangled, messy, a set down.

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A 127mph serve from John Isner leaves Kyle Edmund sprawling and allows the 6ft 10in monster to just dolly a winner away from mid-court.

Another serve up the middle and Edmund finds the bottom of the net this time. It matters little, this next game is the big one as the British man is serving for the opening set.

Smashing some celebratory balls into the crowd was as tough as it got for Novak Djokovic earlier as Mikhail Youzhny was forced to retire after six games. Novak as I've already said has played just four sets to reach round four after two players have been forced to withdraw on him.

He awaits the winner of this match in the last-16 and Novak must feel fresh as a daisy.  

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John Isner turns his head in disgust as he hits a lame backhand into the net at 40-30 down to his 21-year-old rival, that's 4-2.

All he has to do is keep holding now for this opening set, and dare I say it, he looks pretty comfortable out there, as Isner holds in what must have been the quickest game of this set.