Meanwhile, there's an absolute cracker of a match going on over on Court Suzanne Lenglen.

Still work to do. Swiatek can't wrap up the match point at the first time of asking, but she soon has a second chance...

Swiatek swats away that break point and is rewarded as a wayward Liu backhand hands her match point.

Claire Liu isn't ready for this to be over just yet. At 0-15 up, she returns a Swiatek serve superbly.

While Swiatek fights back to draw level at 30-30, Liu confidently comes forward to meet a return and backhands the ball into space for a break point.

Having served for the match a couple of games back, Jannik Sinner finds himself serving to stay in the fourth set.

Daniel Altmaier takes it to deuce but Sinner holds eventually and we will have a third tie-break of the match.

After more than four hours, can Sinner bring it to a close or will Altmaier force a fifth set?

A 14-shot rally - the longest so far of this match - opens up Claire Liu's service game but it goes Iga Swiatek's way - as does the second point.

While Liu pulls a point back - much to the audible frustration of Swiatek - the Pole finds herself with double break point.

Liu hands her the break on the first of those, too much oomph put behind a return.

Swiatek will now serve for the match, and a place in the third round.

It's all square on Court Simonne Mathieu as 12th seed Frances Tiafoe takes the second set. He had to come back from a break down early on against Russian qualifier Aslan Karatsev.

The American has never gone beyond the second round at Roland Garros.

Image source, Getty Images

Relief as Swiatek finally gets the hold on an eight-minute game.

She's two games away from the third round, where China's Wang Xinyu awaits.

Third time lucky? Swiatek sends the ball spinning out of court to hand Liu a third break point and pile the pressure back on her own serve.

Liu wastes her chance though, sending Swiatek from corner to corner across the baseline before netting her own forehand.

Deuce again.

The net gets in the way of converting that break, but a double fault from Swiatek gives Liu a second chance.

Swiatek saves that one off the backhand to take the game back to deuce.

I told you not to get too far ahead...

Successive errors off the Swiatek racquet give Liu a sniff of possible break points but the world number one pings a backhand into the corner to level at 30-30.

But then that break point comes, courtesy of another gorgeous drop shot from Liu that bounces twice for Swiatek can get to it.

Just as she did in the first set, Iga Swiatek goes a double break up.

She wraps it up on her first break point with a magic backhand that leaves Claire Liu stretching into thin air.

Let's not look too far ahead though - Liu got that double break back in the first set, can she do it again?

Jannik Sinner looks to have opened the door for Daniel Altmaier at 0-30 but he quickly rattles off the next two points to make it 30-30.

He has to do it again after offering Altmaier a break point but some sharp work at the net from the Italian takes it to deuce.

Match point... incredible, Altmaier is saved by a net cord! Sinner came in for the volley to finish it off but the ball deflects past him and in!

Second match point - this time Sinner misses long and then Altmaier earns another break point with a cross-court winner.

The German takes it and on we go!

Iga Swiatek carries on at pace to take a 30-0 lead but Claire Liu pegs her back with a delightfully played drop shot off the backhand. Pick that one out.

Swiatek eventually holds to 30 to continue her control of these early stages of the second set.

Iga Swiatek comes out swinging for the second set.

Big-hitting gives her a 0-30 lead on Claire Liu's serve but Liu gets on the front foot to stop her in her tracks...or at least slow her down.

Swiatek patiently waits for a high return to fall, smashing it down into space and the Pole has two break points in the opening game.

She needs only one.

On Court Suzanne Lenglen, Jannik Sinner has three break points but Daniel Altmaier is able to save them all.

But the German misses a gimme to allow Sinner another. Altmaier sends a backhand narrowly wide and the eighth seed will now serve for the match.

Image source, Getty Images

Image source, Getty Images

Here's a recap of the main stories so far from Thursday's French Open action:

• Wimbledon champion Elena Rybakina underlined why she is among the French Open favourites with a convincing win over rising Czech star Linda Noskova.
• Elsewhere in the women's draw, American qualifier Kayla Day knocked out compatriot and 20th seed Madison Keys, winning 6-2 4-6 6-4.
• Russian 16-year-old Mirra Andreeva also progressed, winning 6-1 6-2 against France's Diane Parry.
• Men's fourth seed Casper Ruud moved into the third round with a four-set victory over Italy's Giulio Zeppieri.
• But Australian 18th seed Alex de Minaur exited in straight sets against Argentine Tomas Martin Etcheverry.
• Italian eighth seed Jannik Sinner is currently into a fourth set against Germany's Daniel Altmaier, leading by two sets to one, while American 12th seed Frances Tiafoe is a set down against Russia's Aslan Karatsev.
• In the doubles, Britons Jamie Murray and Lloyd Glasspool have both reached the third round with straight-set victories.
• Murray and New Zealander Michael Venusbeat Colombians Juan Sebastian Cabal and Robert Farah 6-1 7-5, while Glasspool and Finnish partner Harri Heliovaara won against Belarusian Ilya Ivashka and Australian Alexei Popyri 7-6 (7-3) 7-5.

Image source, Getty Images

The first love hold of the match, and it comes at the perfect time for Iga Swiatek.

The world number one wraps up what proved to be a tricky opening set. Claire Liu must go the distance if she's to cause a shock against the defending champion.

Liu lets slip a 30-0 lead but is able to clinch the hold, a backhanded point at the net bringing up game point before Swiatek fires long.

The American puts the pressure back on her opponent to serve out the opening set.