Laura: Almost four hours of blood sweat and tears and still no closer to finding out who will win.

Robert Hinchcliffe: Been focusing on the form of Nadal and Thiem all tournament you forget these two are essentially 1 and 2 in the world now

And he does, despite Wawrinka's 67th winner of the match.

5-5. Who will blink first? No sign of a break in this fourth set so far.

This is just brilliant. The crowd are on their feet. They're lucky to be witnessing this.

The roles are reversed as Wawrinka gets back a Murray smash and plays a lob followed by a drop shot. Copy cat. Great entertainment though.

30-15. Murray needs to hold here remember.

Pat Cash
Former Wimbledon champion on BBC Radio's online-only commentary

Good hold from Wawrinka. It is just going to be a battle of wills.

But, on a clay court, a guy who can defend really well has an advantage over a guy who wants to attack.

Wawrinka matches Murray with a quick service game of his own. He is not shifting easily.

Spare a thought for Rafael Nadal and Dominic Thiem. They've no idea when they're getting on court for their semi-final. Could be another couple of hours yet.

Pat Cash
Former Wimbledon champion on BBC Radio's online-only commentary

Image source, Getty Images

The pressure is straight back on to Wawrinka after that marathon game on his last service game.

Good signs from Murray, he'll be happy to say to Stan: "Come on back on you now, only about a minute after you last served".

Stan gives himself a hefty whack to the forehead as he pushes a sliced return long. Murray will be pleased with the cheap point. Muzza has his opponent on a string the next point with a shot out wide followed by a drop shot.

Wawrinka proves he is mortal by framing one high into the crowd later in the game. That makes us part-time players feel a little better.

Good quick service game for Murray. Very little energy wasted.

Piers Newbery
BBC Sport at Roland Garros

Maybe it's because they want a fifth set, maybe it's because he's a former champion, or maybe it's just because he produces winner after winner, but the Chatrier crowd is very much on Wawrinka's side right now. With their man on the ropes, the loudest roar of the week followed that lunging forehand winner at 30-30. Breathtaking stuff from both men.

Image source, Reuters

Wawrinka went crazy after that passing winner.

Arms pumping everywhere, trying to get the crowd on his side. They responded with another huge cheer. They want this to go to a decider.

Another clenched fist from Wawrinka. He closes the game out.

Pat Cash
Former Wimbledon champion on BBC Radio's online-only commentary

Image source, Getty Images

Oh my goodness. Unbelievable stuff. Murray scraped back another smash to get back into the point and in the end it took an unbelievable passing shot under pressure from Wawrinka. It caught the edge of the line.

Oh my word what a shot!

Murray keeps another point going longer than it should and looks in control when he comes into the net.

Stan has other ideas. He starts the ball in the tram lines and bends it back to land flush on the line.

Murray still fighting though. Deuce.

The Murray fist pump is back.

The Brit gets Wawrinka on the scrambling defence and ends the point by passing Wawrinka at the net. A mental blow. Wawrinka put a lot into that for no return. 30-30.

Chance for Murray to break.

Remember there is nothing to split these two in terms of Grand Slam titles. Whoever wins will be looking for their fourth come Sunday.

Murray has hit less than half the winners of Wawrinka but his 27th of the match takes him to 30-0.

Wawrinka's forehand speed is falling. Just to a pedestrian 80mph.

Good signs for Murray though and so is this. Another drop shot, his sixth of the set. Wawrinka gives up the chase early. He knows he can't get there.

Image source, Getty Images

"Come on!"

No, not from Murray but from Switzerland's Stan Wawrinka.

That was a big hold of serve and he knows it.

Again Muzza wins the first point of the Wawrinka service game, not that the Swiss thinks he has lost the point - he makes umpire Jake Garner go and check the mark in the clay.

Another drop shot from Murray. That's working well at the moment. It helps him move to 15-30.

Oooooooh. Murray has a chance - a very difficult chance - to set up break point with a passing shot but he finds the net. "Make it," Murray says. He's disappointed with that. 30-30.

These two have covered over three kilometres in this match. Remember that is all done in short, sharp sprints. Tough work.

Murray loves it though. He loves to push himself. He's never in any danger in this service game and bats the balls back down in Stan's direction. Over to you.

Image source, Getty Images

Luke Davies: Do we even need the second semi-final? Absolutely brilliant tennis!

Tobias: Andy Murray...the greatest defender since Franco Baresi..what a set of tennis in Paris.

Chanice Hird: AND HE'S GOT IT!!! Andy Murray is 2 sets to the good!!! Come on my boy!!!

Pat Cash
Former Wimbledon champion on BBC Radio's online-only commentary

These overheads from Wawrinka should not be coming back. I'd be disappointed if, even with my old back, I didn't put them away.

Murray gets himself into another service game by battling to 15-30. Wawrinka has been less than comfortable at the net today but he is safe enough here, putting away a volley. 30-30.

It is like Muzza has got in Wawrinka's mind! Twice he guesses the right way to retrieve a smash from his opponent but in the end fluffs a drop shot. Great anticipation nonetheless. Surely that will annoy Stan. He just wants to blast winners and get quick points.

We remain on serve.

Pat Cash
Former Wimbledon champion on BBC Radio's online-only commentary

Against Wawrinka you have to get enough balls back to frustrate him. Murray is one of the greatest defensive players we have ever seen and he is doing that.