An excellent rally early in the game is won by Djokovic with an expertly sliced backhand drop shot volley, picked out from near his feet. Arguably the shot of the match so far.

Djokovic seems to have stepped up a level - his ground strokes are going deeper, pushing Zverev back and not allowing the German to get on the front foot as he prefers.

Then an even better shot by the Serb! A magnificent backhand winner cross court, flashing past Zverev as he tried to advance to the net.

That earns Djokovic his first break point of the match... but Zverev sees it off. Deuce.

Greg Rusedski
Former British number one on BBC Radio 5 Live and BBC Sounds

This is where Hawk-Eye would work.

Alexander Zverev had the same issue in Madrid where he actually took a picture of the mark. I knew he wouldn't do it against Novak Djokovic and this French crowd, but he did make his point.

When we have the technology, I don't always understand why we don't use it.

Image source, Getty Images

Jonathan Jurejko
BBC Sport senior tennis reporter at Roland Garros

Zverev absolutely loves to complain about a line call on the clay.

Again he calls Louise Engzell off her chair, again she tells him where the ball mark actually is.

Cue one of the great pieces of Roland Garros theatre - the Parisians whistling their dissatisfaction at the officials being questioned.

Image source, Getty Images

The two women's singles semi-finals will be played on Court Philippe-Chatrier on Thursday.

The mixed doubles final will kick things off at 11:00 BST - the Italian pair of Sara Errani and Andrea Vavassori face American duo Taylor Townsend and Evan King.

From 14:00 BST - which is when our live coverage will get under way - world number one Aryna Sabalenka faces defending champion Iga Swiatek.

The other semi-final between Coco Gauff and wildcard Lois Boisson will follow immediately afterwards.

Djokovic brilliantly passes Zverev as he steps into mid-court and pummels a forehand winner past the German.

Then in the following rally, a flashpoint as Alexander Zverev claims a winner from Djokovic was out - but Louise Engzell descends and points out the mark is part on the line, amid whistles from the crowd.

Djokovic then hits his second ace of the match, before getting a big net cord in his favour to take the game.

Image source, Getty Images

Novak Djokovic deployed the drop shot often early in this match - five times in the opening couple of games - but has now retreated more into rallies from the baseline as we have moved into the middle of this set.

But that should benefit the more powerful Alexander Zverev, who has hit nine winners already.

A couple of wild hits from the German, but a big serve at the right time - jammed into Djokovic's body - sees him hold to 30.

Jonathan Jurejko
BBC Sport senior tennis reporter at Roland Garros

Djokovic's first serve has become an increasingly fundamental tool as the years have rolled on.

The precision of his opening shot is so effective and stalls the momentum of his opponents - as we saw in the early part of the fifth game.

Image source, Getty Images

Greg Rusedski
Former British number one on BBC Radio 5 Live and BBC Sounds

Novak Djokovic has to serve well today because he has got to be able to get on the front foot and get the first strike.

If Alexander Zverev is allowed to get the first strike, Djokovic is going to have a hard time trying to win this match.

We have our first contentious line call, with Louise Engzell descending from her chair to confirm a shot from Zverev was indeed just too long.

It allows Djokovic to serve out the game and stay in touch.

Image source, Getty Images

Novak Djokovic's bid for a standalone record 25th Grand Slam singles title continues tonight.

He is competing in his 62nd major quarter-final, and aiming for his 51st career semi.

When he gets his first serve right, it is a mighty weapon for Zverev. He has averaged 130 mph at this tournament.

From 30-30, he sends two exceptional efforts down the T which Djokovic can only spiral into oblivion.

Greg Rusedski
Former British number one on BBC Radio 5 Live and BBC Sounds

I'm looking at that electric yellow that Alexander Zverev is wearing and I'm thinking it should be an illegal colour. The ball gets lost in there when you're looking at it.

I'm not a fan of it and I think it should be banned.

Image source, Getty Images

No confusing the two men out on court tonight. Novak Djokovic is wearing a bright red polo shirt, while Alex Zverev is in fluorescent yellow with equally garish trainers.

The man in red has arrived in this match, holding to 15.

Image source, Getty Images

Jonathan Jurejko
BBC Sport senior tennis reporter at Roland Garros

Djokovic's tactics are quite clear. He doesn't fancy getting into lengthy baseline exchanges if he doesn't have to.

After bringing out the drop shot early doors, he goes on the attack in the opening game.

Djokovic tries to push Zverev out wide on the forehand before going down the line on the other wing.

The problem was, though, being a little too aggressive with his returns.

Zverev consolidates his break, holding to 15.

A solid start by the German - let's see if he can maintain this level. That has been his failing in so many big matches in the past.

Greg Rusedski
Former British number one on BBC Radio 5 Live and BBC Sounds

I think that is the perfect start for Alexander Zverev.

It was interesting from Novak Djokovic because his tactic from early on was to go into the forehand side of the German and break it down, but it didn't really work.

It's always a little worrying when Djokovic starts with the drop shots in the opening game.

Alexander Zverev with the early break, but he isn't totally satisfied - he hands his racquet to someone in his support staff in the stands. It looks like he wants the handle grip redone.

Another rally, Djokovic slides to reach a crosscourt backhand - and sends it wide.

Early blow in favour of Zverev.

Already this match has potential classic written all over it.

Novak Djokovic has hit one terrific winner - but an overhit backhand opens the door for his foe...

Image source, Getty Images

Jonathan Jurejko
BBC Sport senior tennis reporter at Roland Garros

Djokovic has got the head and got the heart at Grand Slams - but has he still got the legs?

That's the big question after he celebrated his 38th birthday a couple of weeks ago.

Zverev, who is decade younger at 28, has got the legs - but sometimes not the head or the heart.

That particularly applies when he's playing in a Grand Slam final, having buckled under the weight of his own expectation in three showpiece matches.

In terms of quarter-finals, Zverev has won nine of 15 - including seven of the past nine.