Here we go, a couple of well-worked points from Novak Djokovic and he's got two break points.

He nets the first but Joao Fonseca still has another to face...

Annabel Croft
Former British number one on BBC Radio 5 Live

Djokovic looked absolutely drained throughout that entire point and he still managed to manipulate Fonseca.

That'll be just what Djokovic needs, a relatively straightforward service hold.

He even wins a bizarre point in which he almost forgets to move for the ball and ends up awkwardly reaching for it and stabbing it over the net.

Joao Fonseca makes no mistake about holding this time, beginning the game with a beautiful drop shot that even Novak Djokovic has to applaud.

Djokovic is bending over a lot between the points. What has he got left in the tank?

Annabel Croft
Former British number one on BBC Radio 5 Live

Djokovic is fighting hard. He is suffering big time.

Novak Djokovic is wiping his brow and stands hunched over his towel box in between points but is enjoying a much more dominant position on the baseline during the rallies.

Encouraging signs as he holds to 15. He leads 3-2 in the fourth set.

Image source, Getty Images

And there it is! Novak Djokovic steps inside the baseline to receive a second serve and his powerful return is too much for Joao Fonseca.

We're back on serve on Philippe-Chatrier.

Joao Fonseca is coming up with all of the shots! He chases down a drop shot, forces Novak Djokovic into a smash, and then plays a delicate drop winner of his own which spins away from the Serbian - simply lovely. 30-0.

However, if there's one man who doesn't know when he's beaten, it's Djokovic and with the help of a couple of errors from the teenager, he's got a break point.

Annabel Croft
Former British number one on BBC Radio 5 Live

Djokovic is trying to ignite the fire with his anger.

Image source, Getty Images

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?