This match also sees two Grand Slam champions go against each other in the support box.

Murray's coach Ivan Lendl against Nishikori's Michael Chang. Both former French Open winners.

Chang will be pleased with his player's start to this set as he holds serve.

If Stan Wawrinka was a top-of-the-range saloon car, he'd be motoring along in cruise control right now.

The Swiss third seed, already a set up, breaks Marin Cilic's serve in the third game of the second set to move ahead again.

Image source, EPA

A quick look at the stats again.

Kei Nishikori only made 27% of his first serves in that set. You're not going to win any top level match with that statistic.

Throw in 13 unforced errors and the Japanese player's fans could be forgiven for being a little concerned.

Barry Flatman
Sunday Times tennis correspondent on BBC Radio 5 live

I said at the end of the first set that Murray needed to up his game. He didn't really have to do that. Nishikori did it for him.

It now makes it more of a contest.

Image source, AFP

Piers Newbery
BBC Sport at Roland Garros

We have a rather surprising spectator on court in Simona Halep, fresh from her news conference after reaching the semi-finals earlier this afternoon. Spurning the chance to go to the gym, or put her feet up, the Romanian is sitting alongside compatriot and all-round tennis mover and shaker Ion Tiriac, as well as her Aussie coach Darren Cahill. She clearly cannot get enough tennis.

Image source, Reuters

Murray squares things up on his serve, hitting a delightful drop shot along the way.

This really is a topsy turvy match. From the extreme of Nishikori dominating the first set to Murray breezing through the second.

One thing is for certain. That set changed after that interjection from umpire Carlos Ramos.

Image source, AFP

Emily: Murray constantly makes me stressed and I'm only following the live text at work and trying not to react to dramatically.

Deletsu: I love Murray as much as the next guy but my, he always has something to complain about. Always!!

Nishikori saves the first break point with a perfectly timed forehand up the line.

Oh Kei, what have you done!? He's in prime position to save the second with the volley at the net but chooses to leave the ball. It drops in and Murray has the double break. It was easier to hit the ball than leave it.

The frustration is starting to show from Nishikori now as he makes another couple of errors. Head thrown back.

He must be wondering what has changed from the first set when he was dominant.

Murray finds another good angle with the forehand to bring up two more break points.

Alice Stainer: Nishikori dressed like a boy scout & obviously prepared...but given crazy tide turn in Halep match I'm not panicking for Andy yet.

Joshua Byers Warner: I really don't understand Murray! He is struggling because he is not trying!

Stan Wawrinka has been enjoying himself in Paris over the past week or so. And not many people have noticed.

The Swiss has flown under the radar somewhat, well, as much as a third seed and former champion can fly under the radar.

He hadn't dropped a set at Roland Garros going into his quarter-final against seventh seed Marin Cilic.. and he still hasn't.

Wawrinka seals the first set with an ace.

Image source, Getty Images

Break point saved with a good change up on second serve from Murray.

But now a fourth double fault from the Scot. A second chance for Nishikori.

That's a bad miss. Murray clips the tape and the ball sits up lovely for Nishikori to slap away but he nets.

More shouts from Murray. "Let's go." He bounds back to his seat after increasing his lead in this second set.

Barry Flatman
Sunday Times tennis correspondent on BBC Radio 5 live

The quality has dropped dramatically in this set.

Nishikori has gone from a creditable 9.5 out of 10 to somewhere like a five or six.

Both players are struggling a little with their serve. Murray doesn't really get close to getting his second effort over and double faults for a third time. 15-30.

Nishikori is a little more inconsistent now but still dangerous. Some good hitting brings up another break point...

Image source, Getty Images

Jamie Taylor: That "loss of serve" penalty for taking too long to serve might be the fire up Muzza needs. Come on Muzza!

Raj Sidhu: Hahaha, love how the time violation actually helped Murray

Double fault from Kei Nishikori.

He is not happy with the umpire. That interjection has really got Murray going.

Now can he consolidate the break?

Image source, PA

Murray is chirping away at himself now. He's in the zone.

Nishikori puts a backhand in the net - he's not done that often - and now Murray senses an opportunity 15-30.

Nishikori long with an overhead!

"Yes," Murray says to himself.

Two break points coming up...

Barry Flatman
Sunday Times tennis correspondent on BBC Radio 5 live

They’ve been clamping down on time violations at this tournament.

Sad as though it seems, the only way to do it is to get a clock on the court.

That might have done Murray a favour. It might have got him into gear.

Piers Newbery
BBC Sport at Roland Garros

"Allen On-dee!" The home crowd are getting behind the Brit as they sense an unexpectedly free evening looming, Nishikori has been so dominant. It might have taken a time violation to get the adrenaline flowing both on and off court, with Murray roaring "Let's go!" and the crowd responding. Meanwhile, Lendl remains unmoved. Obviously.

Image source, Getty Images

Forehand winner Murray. Again he tries to get himself going, "come on, come on," he says.

Backhand missed. That should have been buried. Deuce again.

Now Murray is not amused. Carlos Ramos in the umpire chair calls time violation as Murray pulls out of a serve.

"I have never seen that," Murray says to him.

That has fired the Briton up. The game won with a HUGE forehand.

A classic Murray fist pump and scream aimed in the umpires direction.

Is that the spark Murray needed?