There it is. Zverev picks his spot with a backhand to wrap up the opening set.

Plenty for Carlos Alcaraz and his team to ponder after that 44 minutes of play.

Image source, Getty Images

The 'ooohs' and 'ahhhs' are beginning to flow from the crowd as the players exchange blows.

But it's Zverev who has two set points.

David Law
Commentator on BBC Radio 5 Live Sports Extra

These are regulation rally balls that Alcaraz is missing at the moment. I don't think Zverev can believe his luck.

Alcaraz turns his back and flips is racquet as a backhand loops long. Another miss, and Zverev is closing in on the set.

Naomi Broady
British player on BBC Radio 5 Live Sports Extra

It's a very subdued crowd because there are so many Spanish flags in support of Alcaraz.

He's had 14 unforced errors in this opening set, compared to Zverev's six.

Alcaraz smashes at the net for a second time, making no mistakes on this occasion. Zverev would have to be twice as tall to reach that one.

Again the German stays in touch, but Alcaraz jabs the air as a flat forehand flies down the line for 40-30. A miss from Zverev, who is made to serve for the set.

Alcaraz gets stuck into a second serve from Zverev, but the German defends well to prevail in a 17-shot rally, by far the longest of the match so far.

Zverev cracks a 130mph serve to seal a love hold. He's just one game away from the opening set and looking comfortable.

Don't they grow up quickly...

With Holger Rune and Carlos Alcaraz both in the last eight, this is the first time two teenagers are in a Grand Slam quarter-final since 1994.

That was also at Roland Garros, with 19-year-olds Hendrik Dreekmann of Germany and Andrei Medvedev of Ukraine making the last eight.

If junior team-mates Rune and Alcaraz are to meet in the main draw singles at Roland Garros, it would have to be in the final.

This has been an impressive start from Zverev, who continues to stay uncomfortably close to Alcaraz. He can't quite take the Spaniard the distance on serve this time, whipping a return long. Relief for Alcaraz.

Jonathan Jurejko
BBC Sport at Roland Garros

Very little, if any, interaction from Alcaraz's coach Juan Carlos Ferrero during that fifth game where the Spanish player lost his serve.

The teenager had a little chunter to himself early in the sixth, too.

Now at the same end as his box - which is packed with his team and family - Ferrero leans forward on his forearm, other hand stroking his chin.

Looks like a man people watching from a cafe on the Costa Blanca coast.

Allowing Alcaraz to problem solve is a key part of his education from Ferrero and the 2003 Roland Garros champion is not yet feeling the need to get involved.

Alcaraz mumbles in the direction of his team as a forehand nestles into the net.

Early signs of frustration from the 19-year-old, who hasn't been allowed to settle yet.

There's plenty of time for popcorn-worthy tennis yet, Naomi.

But Alexander Zverev isn't interested in any of that for the time being. He keeps the points short on serve to move to 40-0, before a whopping forehand gets Alcaraz on the board.

That's all he'll get though. Zverev consolidates the break.

Image source, Getty Images

Naomi Broady
British player on BBC Radio 5 Live Sports Extra

It's the first time I've watched Alcaraz in a long time when I haven't thought he looks invincible.

I'm interested to see how he is mentally as this match progresses. He's usually so poker-faced but we've already seen a little bit of frustration poking through.

I know it's still early days, but I'm almost a little disappointed. I had my popcorn ready for this one.

Image source, Getty Images

Alexander Zverev makes the first breakthrough!

The German refused to go away, building pressure and eventually taking a third break point opportunity.

The third seed has settled in nicely.

Jonathan Jurejko
BBC Sport at Roland Garros

Earlier in the fifth game Alcaraz played a drop shot which he probably didn't need to.

But it was a useful one in terms of sharpening his touch.

That is what we saw when he knocked another in from the baseline.

Already a shot which is one of his trademarks.

Naomi Broady
British player on BBC Radio 5 Live Sports Extra

I'm assuming it's just nerves out here. Alcaraz, especially, knows how big a step it would be for him to reach a semi-final. Maybe he's feeling the pressure a bit.

Zverev clips a forehand down the line and Alcaraz can't lift it back over.

The first big shout from Alcaraz! He follows up a big serve with a drop shot for deuce.

Stop ittt! Anything you can do, says Alcaraz.

Another devastating drop shot catches Zverev out as the Spaniard moves 30-0 up on serve, but a wayward backhand flies off into the tramlines to bring Zverev level.

A couple of scorching serves put Zverev in control on serve. No hope for Alcaraz there.

It shapes up to be another satisfying service game for the German third seed, who drifts in a wonderful, angled drop shot to clinch a love hold.

Image source, Getty Images

Naomi Broady
British player on BBC Radio 5 Live Sports Extra

It looks like Alcaraz is rushing these points a little bit, he's snatching at a few shots, and his unforced error count is getting a little high.