I doubt wither of these two thought they'd be kicking-off just before midnight, but here they - and we - are.

So that's the end of a marathon session - thanks for joining me for it, and do join us again tomorrow!

Mertens is a rock and in no time leads 0-40 ... and Gavrilova nets a forehand! Mertens comes back from 0-5 down in the first set to win in two, and the number 23 seed is out!

Gavrilova earns three break points but can't take any - bits I also missed. Mertens has played the key points superbly, but again, it's Gavrilova with advantage, and a double fault sees her claw back one of her two breaks!

My apologies - my system crashed and I've only just been able to get back in, but Mertens is serving for the match!

Gavrilova digs deep to reach 30-all from 30-0, but a clubbing forehand from Mertens gives her game point and then Gavrilova nets a backhand. Mertens has serious moxie.

Mertens is making Gavrilova fight for everything now - of course Gavrilova is up for it. She holds to 30, and appear to have arrived ar some kind of intra-game contest.

Love hold for Mertens, who's looking very comfy indeed.

Gavrilova finds something and wins her first game in eight, to 15. She took a comfort break between sets and perhaps got her head straight while in the dunny, a circumstance with which I imagine we're all familiar.

Gavrilova is not a good a moment and in losing the first point of this crucial game seems half-arsed. I'm sure that's not true, though it's quickly 30-0, and then after a longer rally, she drags a forehand wide. Three set points! Mertens messes up the first by hitting a forehand long for no real reason ... only to snaffle the second! Wow! this is not something you see very often!

The pressure is on Gavrilova now, and she zones a backhand slice wide to cede the lead in this game, then goes long with one! Oh gosh! But Gavrilova then finds a lovely forehand angle to whip cross-court ...only to lose the next point and throw in a double! MERTENS WILL SERVE FOR A SET IN WHICH SHE PREVIOUSLY TRAILED 0-5!

Gavrilova is swinging for the fences now, and this renewed vigour gets her 0-30 ... and at the end of a brutal rally, one looped across the face of the net, off the frame, arranges three set points! Mertens saves the first two, then Gavrilova goes long with a return! The points are getting longer now, as both players are playing at the same time, but Mertens is still in the ascendancy and it's 5-5!

Well! Gavrilova starts with a double ... but recovers with an ace down the middle. She's then pegged back to 30-30, but a service winner earns her first set point ... only for Mertens to get the better of an exacting rally, a backhand down the line sealing the deal; deuce. Oh really! Gavrilova sends down another double ... then another! She chucks her racket and dearie me! Mertens is one hold away from a 0-5 comeback!

Gavrilova reaches 15-30 but a drive-volley from Mertens hauls her back, and when Mertens wins the next point too, she looks pensive ... until a forehand from corner to corner takes us to deuce. Mertens isn't cowed though, and quickly closes out; Gavrilova will now serve for the set a second time.

Whaddaya know, Mertens is fighting back and gets to 15-40, then guides backhand at toes! Gavrilova can only net, and has momentum switched?

Mertens just isn't at it at all, but she plays a nice point to reach 30-all as a feather falls and Gavrilova complains after the fact. Can she build on it? Well a drop shot forces a poor lob, which she puts away well, only to then slice into the foot of the net and concede deuce. That was a very poor shot indeed. Anyway, Broady tells us that when she played Gavrilova last year the crowd were shouting "Smash her, Dasha" but she can't quite pull it off here, missing four set points before Mertens gets ehrself on the board.

Mertens isn't going away, though, and gets herself to 30-40 only to tamely overhit a forehand. And then she guides a forehand volley into the net before netting a return - she's just so tentiatve at the moment, and Gavrilova isn't the kind who waits to be asked.

Gavrilova is away here and gets 0-30, after which Mertens goes long with a forehand to present three break points. She saves the first, but then goes long with another forehand, and this set is effectively did.

Mertens makes Gavrilova fight for her consolidation, but she gets there in the end as Naomi Broady discusses how fun she is off the court. That is nice to know.

In commentary, Naomi Broady talks about how much she enjoys Gavrilova and the expressive way she plays, rather than the po-faced manner of others. Anyway, she gets to 30-all and then unleashes an inside-out backhand down the line for break point - both players have better back than forehand, says Broady, and she's expecting to see them go down the line. Gavrilova is then forced to challenge a call saying she hit long - she's right - and they replay the point. She pounds a cross-court backhand close to the tramline, Mertens challenges, ands she's right too; deuce. They then exchange advantages, Mertens ruining hers with a double, and then after saving another break point, the pressure tells. First blood to the Ocker!

Gavrilova serves and chucks in two double faults, but those are the only two she loses in the game.