We're going the distance on Court Philippe Chatrier!
Iga Swiatek has certainly raised her level and serves out the second set to love just before the two-hour mark.
Image source, Getty ImagesSabalenka 7-6 (7-1) 4-5 Swiatek*
Andrea Petkovic
Former world number nine on BBC Radio 5 Sports Extra and BBC Sounds
I think Iga Swiatek will serve this out.
Her serve has tremendously improved in this second set. It was really her downfall, that kept her on the back foot, in the first set but she has found more rhythm, more accuracy and more pace on it.
Sabalenka 7-6 (7-1) 4-5 Swiatek*
Aryna Sabalenka shouts at herself after finding the net despite getting stuck in to Iga Swiatek's opening point.
She then looks to the sky after failing to finish Swiatek off at the net as the fifth seed wriggles clear. Three set points.
Sabalenka 7-6 (7-1) 4-5 Swiatek*
Aryna Sabalenka does what she must, holding to 15 with another brutal serve to force Iga Swiatek to see this set out.
Can Swiatek hold her nerve? Closed eyes and a deep breath for the defending champion at the change of ends.
Image source, Getty Images*Sabalenka 7-6 (7-1) 3-5 Swiatek
Andrea Petkovic
Former world number nine on BBC Radio 5 Sports Extra and BBC Sounds
The scoreline is making the dynamics of this match interesting.
Aryna Sabalenka actually went over to check the mark of her serve, which Iga Swiatek had a discussion with the umpire about, and she didn't even look convinced it was in. She laughed at it!
You can see every emotion in her face. She doesn't have the ability to control it. She would be a terrible poker player.
*Sabalenka 7-6 (7-1) 3-5 Swiatek
These two are going toe-to-toe now! A rare lengthy, 12-shot rally goes the way of Iga Swiatek - as does this latest game as the defending champion closes in on the second set.
This is simmering nicely as, it now seems, we edge towards a decider.
Image source, Getty Images
Jonathan Jurejko
BBC Sport senior tennis reporter at Roland Garros
It wouldn't be Roland Garros without one player - if not both - complaining about a line call.
Swiatek is adamant about that Sabalenka serve but French umpire Kader Nouni disagrees.
He doesn't even want to get down off his perch on this occasion to discuss the ball mark.
The usual chorus of whistles ring in Swiatek's ears and, after Sabalenka holds, even she goes round the net to take a look.
The shrug indicates she think she's got away with one.
Sabalenka 7-6 (7-1) 3-4 Swiatek*
Iga Swiatek is unhappy - to say the least - with the chair umpire, after calling a ball out but being dismissed.
Probably for the best if she doesn't find out that, according to Hawk Eye technology, she was correct.
It doesn't have much of an impact in this latest game anyway, as Aryna Sabalenka extends the run of holds with a swift four points to stay within striking range.
Image source, Getty Images*Sabalenka 7-6 (7-1) 2-4 Swiatek
Andrea Petkovic
Former world number nine on BBC Radio 5 Sports Extra and BBC Sounds
Iga Swiatek has definitely found her rhythm on serve.
She is serving freely. She is getting more pace on it. She is finding more accuracy on it. It has changed this entire game around.
The serve is like a virus, it can infect your game when it is bad.
*Sabalenka 7-6 (7-1) 2-4 Swiatek
Aryna Sabalenka is chasing shadows at the back of the court as Iga Swiatek locks in and really begins to hit her stride.
The clean winners are beginning to flow for Swiatek now and she crashes down an overhead which bounces way over Sabalenka for straightforward hold.
Three holds of serve in a row?! What is going on?
Image source, Getty ImagesKaplan/Ramphadi 6-3 2-6 Lapthorne/Schroder
It was a disappointing start to the day for British quad men's tennis hope Andy Lapthorne, as he lost in the singles semi-final to top seed Niels Vink of the Netherlands, 6-4 6-4.
He's looking to make amends in the doubles semi-finals right now alongside Dutch partner Sam Schroder - the duo are the second seeds.
After losing the first set to Ahmet Kaplan of Turkey and South Africa's Donald Ramphadi, Lapthorne and Schroder won the second in just 33 minutes.
It's down to a decider on Court 13.
Jonathan Jurejko
BBC Sport senior tennis reporter at Roland Garros
While the serving has clearly not been top drawer, the number of breaks is as much down to the quality of the returning.
Both players have been off the scale in that department.
Sabalenka 7-6 (7-1) 2-3 Swiatek*
Aryna Sabalenka steadies herself with a comfortable hold of serve to love to remain in touch in set two.
Increasing signs that this is now becoming the high-quality blockbuster everyone hoped for.
Image source, Getty Images*Sabalenka 7-6 (7-1) 1-3 Swiatek
A real touch of class from Iga Swiatek, who scoops a delightful drop shot over for 40-15.
Oh, but that's even better!
In a match which has so far been dominated by errors and tension, Swiatek makes another drop shot to complete the hold with the two standout points of the contest so far.
That will undoubtedly boost her confidence as she tries to pull away and force a decider now.
Image source, Getty ImagesSabalenka 7-6 (7-1) 1-2 Swiatek*
We await a first hold of serve in set two, but if Iga Swiatek can achieve that here she'll be halfway to levelling the match.
The four-time champion produces an ace - her first of the match - to avoid facing immediate pressure after going 0-15 down.
Sabalenka 7-6 (7-1) 1-2 Swiatek*
Andrea Petkovic
Former world number nine on BBC Radio 5 Sports Extra and BBC Sounds
Aryna Sabalenka is just trying to go down the line too early in the rally.
It is the cheap points that decide matches in the end, not the highlight reels.
You will see plenty of players in the highlight reels that never won Grand Slams.
Hear BBC radio commentary via the "Listen live" link at the top of this page.
Sabalenka 7-6 (7-1) 1-2 Swiatek*
Already 21 unforced errors by Aryna Sabalenka and 26 for Iga Swiatek tell you all you need to know about the pressure these two are feeling out there.
A series of misses by Sabalenka hand Swiatek three break points, and it's not long before another unforced error from the top seed finishes off a break to love.
Image source, Getty Images*Sabalenka 7-6 (7-1) 1-1 Swiatek
A real gift from Iga Swiatek after making such a promising start to the second set.
That's wide and Aryna Sabalenka is level after a 10th break of serve in this match.
Image source, Getty ImagesSabalenka 7-6 (7-1) 0-1 Swiatek*
Andrea Petkovic
Former world number nine on BBC Radio 5 Sports Extra and BBC Sounds
I feel like Aryna Sabalenka is playing particularly quick between points because she knows that Iga Swiatek has her routines and rituals.
In that first service game, Sabalenka was stood up at the baseline and ready to serve very quickly after the previous point had ended.
Tennis is a psychological game - and those are the types of games you have to play.
Sabalenka 7-6 (7-1) 0-1 Swiatek*
Aryna Sabalenka has not really got going yet after taking the first set, but she battles her way to 30-30 by outlasting Iga Swiatek in a baseline exchange before the defending champion misses to gift her opponent a chance to break back.