Williams wins 3-6 6-4 6-2
Williams now leads head-to-head 16-3
Serena to play Sloane Stephens next
Williams aiming for third French Open title
We are all done. It has been a day long on quality and duration.
Wins for the old guard of Andy Murray, Novak Djokovic and Rafael Nadal as young guns like Nick Kyrgios and Thanasi Kokkinakis are made to wait their turn.
We'll be back tomorrow. The pick of the matches then is a mouth-watering Roger Federer against local rabble-rouser Gael Monfils.
See you then.
That result completes the last 16 line-up. This is what we are looking at:
Serena Williams v Sloane Stephens
Sara Errani v Julia Goerges
Petra Kvitova v Timea Bacsinszky
Andreea Mitu v Alison Van Uytvanck
Ana Ivanovic v Ekaterina Makarova
Elina Svitolina v Alize Cornet
Flavia Pennetta v Garbine Muguruza
Lucie Safarova v Maria Sharapova
The handshakes between the pair are friendly enough after Williams has completed a pirouette of delight.
There is a little exchange and agreement as they head to press umpire flesh, as if to say "we're still cool aren't we?".
The end comes suddenly and swiftly.
Victoria Azarenka pumps a backhand wide to offer up two match points and Serena Williams takes the first with a superb angled forehand.
Image source, Getty ImagesSerena Williams has got the momentum of a landslide now.
She holds to love with an ace to crown the game and Victoria Azarenka is raging against the dying of the light.
She thrashes a ball into the stands in frustration midway though the game, and is fortunate to escape a point penalty. Not that it would have made any difference beyond shortening her suffering.
Image source, Getty ImagesIt is apparently five years since Victoria Azarenka lost a Grand Slam match after winning the first set.
Serena Williams was the person who beat her on that occasion though.
Victoria Azarenka cannot prise a deep top-spinning forehand off the deck and offers up a break point at 30-40.
A horrible framed forehand by Azarenka flies long. Serena emits a gleeful and slightly unsporting squeal in delight.
The American is a break up and her odds are shrinking fast.
Image source, Getty ImagesThirty-all and the stakes are stratospherically high.
Victoria Azarenka cranks up the power, but her forehand tugs off the leash and streaks into the net.
Williams batters a serve down the middle and Azarenka's fend floats long under the American's careful gaze.
There is the snarl. Serena Williams booms away a winner for a 0-40 lead.
Time for Victoria Azarenka to strap on the crampons and try to climb out of the abyss again.
A popping serve clears one of the three break points off the table, but a tug wide into the tramlines put us back level.
Image source, AFPSerena Williams steadies the boat with a hold of her own.
Azarenka ahead on the scoreboard, but crumbly in the top six inches. Williams with the pedigree, but a shade under the weather.
Put those factors through your tennis supercomputer and tell me what you come out with. I'm stumped as to where it is going.
Piers Newbery
BBC Sport at Roland Garros
"There's nothing the Roland Garros crowd like more than a bit of drama, and the end of that second set provided some of the best we've seen this week.
"Azarenka's waving away of Williams' explanation over the line call did not go down well with the American, who sat on her chair during the changeover shaking her head while Azarenka headed off court to cool down. The friendship between these two appears to be on hold for the moment."
Image source, ReutersA rock-solid hold from Victoria Azarenka.
Serena Williams white-washed to love.
A statement of intent.
Image source, APVictoria Azarenka clearly doesn't see the odds the same way I do.
A whipcrack return in the very first point of the decider and she is rapidly into a 0-40 lead.
Azarenka gets exasperated with the umpire as he gets out of his chair and calls a marginal mark against her.
The crowd get on the Belarusian's back - there is call of "just play" from the cheap seats - and she duly does, winning the next point to take an early break.
All very well at the easy end of a set. Can she do the business at the pointy end of things?
Into a final set.
Where's your money on this one? I think momentum, pedigree and history make it a 70:30 call in favour of Williams.
Serena Williams' entourage are up and out their seats as their woman inches forward and hits a devastating return winner for 0-30.
All on the front foot now. Williams advances to bury a backhand for 0-40. Three break points and the sort of mountain you need oxygen for between Azarenka and safety.
She has made it though. Two whopping serves and then a Williams forehand tightrope-walks down the wire before dropping on its owner's side. Deuce.
A duffed Azarenka drop-shot lands her straight into the sticky stuff. A fourth break point.
Controversy! Azarenka hits deep and Williams nets in response as a line judge mistakenly calls out at the same instant.
Azarenka insists it should be her point. The umpire orders a replay. Williams wins that, Azarenka turns the air blue and we are into a decider.
Image source, APSerena Williams, with a bit of strut, swagger and spring in her step now, ramps up to 40-0.
Victoria Azarenka is able to apply a bit of pressure as she nicks the next two points, but that Williams service action is purring now.
It is chugging along and the production line of aces is back up and running.
Serena Williams takes the first point. Victoria Azarenka's service winner ties down the second point. 15-15.
The nerves are almost audibly creaking now. The crowd are hushed, it feels uncomfortably like rubber-necking as Azarenka's composure is tested to destruction.
A jagging Williams forehand. 15-30. Azarenka into the net. 15-40. Two break points.
Williams now getting twitchy. Into the net she goes. 30-40.
Azarenka long!
I've got a nasty feeling this is not going to be over any time soon.
Image source, AFPPiers Newbery
BBC Sport at Roland Garros
"We're approaching the moment of truth here - can Azarenka put her Madrid nightmare behind her and get over the line? Team Serena looks pretty glum in the stands, with coach Patrick Mouratoglou managing not much more than a clenched fist, but his charge is doing her best to get pumped up when the opportunity arises.
"Azarenka is a two-time Australian Open champion, so she knows how to win big matches, it's just been a while."
Serena Williams' service games are ticking along nicely now. An ace seals a hold to 15.
But Victoria Azarenka doesn't need to go hunting any more. She has bagged her break and now just needs to make it back to base unscathed.
The Belarusian pulls a fresh stick out of the cellophane to serve in the next...
Victoria Azarenka finds a big serve in her quiver just when she needs it to pull herself back to 30-30.
But Serena Williams is swatting everything she can get decent play on from the back of the court.
An enormous backhand skids away for a clean winner from a foot behind the baseline to bring up break point.
Williams' attempt at something similar on the next point lands plum between the tramlines. Azarenka worms off the hook and nabs the game.
She is two service holds away.
Image source, AFPSerena Williams takes her aggression out on the ball.
Big, savage baseline hitting as Victoria Azarenka allows her to plant her feet and blast grenades.
Has that final rally hooked up the jump leads to the American's misfiring game? It was an ominous little exchange for Azarenka to go and stew on during the changeover.
Image source, AFP