Novak Djokovic has been shaking his arm and rotating his shoulder quite a bit early in this fourth set.

Joao Fonseca wallops a backhand winner from halfway up the court for 40-30 but Djokovic completes the hold, not that you could tell from his expression.

The crowd is getting rowdy, receiving multiple pleas to keep it down from the umpire.

Novak Djokovic is trudging around at the back of the court between points and wearing a heavy frown.

As for Joao Fonseca, his tail is up. A hold to 30 is celebrated with an energetic shake of the first.

Annabel Croft
Former British number one on BBC Radio 5 Live

Djokovic couldn't cope with the pace. It looks like he is being pushed backwards and he is not enjoying this feeling.

Image source, Getty Images

Having also seen his level drop in the third set against Valentin Royer, Joao Fonseca pulling the match back to 2-1 wasn't entirely unexpected.

However, the Brazilian has broken in the opening game of the fourth and Djokovic is beginning to look a bit weary.

Joao Fonseca earns a fifth break point after Novak Djokovic nets a forehand.

As he sets up for his serve, down advantage, Djokovic receives a time violation from the umpire.

Joao Fonseca is pounding groundstrokes at Novak Djokovic, driving the 39-year-old into the corner of the court.

Eventually, the Serbian hits the ball long, gesturing in frustration. Back to 40-all we go.

Ace! Huge serve in the context of the match.

After all that good work, Novak Djokovic sends a forehand long.

Joao Fonseca wastes his first break point, overcooking a cross-court forehand into the tramlines, and then nets a forehand return.

Is it going to be third time lucky?

Nope. Novak Djokovic reads Fonseca beautifully and gets a racquet on the end of a ferocious forehand, pinging the ball into the space the Brazilian had vacated. Deuce.

Well, erm, it's not looking great for the Serbian at the moment.

Novak Djokovic has been completely overpowered by young Joao Fonseca and is facing three break points in his opening service game.

One service box on each side of the net is in shade on Court Philippe-Chatrier as Novak Djokovic gets the fourth set under way.

The 39-year-old won his previous two matches in four sets. Can he regroup and do the same again?

Image source, Getty Images

Such a tense game, such an entertaining match.

Even Novak Djokovic has to smile when Joao Fonseca hits a brilliant drop shot to stop himself going 30-0 down.

Djokovic fights back to earn a break point but misses the return on Fonseca's second serve.

Fonseca then blasts two aces to clinch the second set.

Annabel Croft
Former British number one on BBC Radio 5 Live

I think Fonseca is playing the best tennis I have ever seen him play. He is more than holding his own here.

Both players are using bags of ice to cool their bodies down at the changeovers. It's still pretty hot out there although Djokovic has now taken his cap off.

At 39, Novak Djokovic will not want to use up too much energy but he also needs to make sure he gets the job done.

It looks like he is being pretty efficient in this service game, as he goes 40-0 up before Fonseca pegs him back to deuce.

But he does eventually hold.

Now Joao Fonseca will serve for the second set - let's see how the 19-year-old copes with the pressure.

Joao Fonseca is absolutely walloping that forehand.

The 19-year-old needs just one more game to take the set.

Another straightforward hold for Novak Djokovic.

Now he needs get to work on Joao Fonseca's serve.

Joao Fonseca is hitting the ball so hard.

The young Brazilian holds again, securing the game with a ferocious forehand, followed by an even more ferocious roar.

After some lung-busting rallies in the previous game, Novak Djokovic will be pleased to hold with four quick points.

The match-time has just turned two hours.

Annabel Croft
Former British number one on BBC Radio 5 Live

This crowd are being treated to something different every single match. This is absolutely jaw-dropping what we are witnessing here.