Both players show their frustration here in what looks like being a pivotal game. Muguruza squanders two game points from 40-15 and looks up in desperation at her coach Sam Sumyk. Halep battles her way to a break point up advantage but slams her racket after sending a forehand long. She's then muttering at her box after wasting a second break point moments later. Halep's mood worsens further as Muguruza reels off the next two points to dig out the hold. 

Three games in a row for Muguruza. 

A momentum change? Possibly. Muguruza is on fire this game, prowling around the baseline and ripping away an 80mph forehand winner to earn two break points at 15-40. A stinging return then draws an error from Halep, and Muguruza has the break. 

Game on?

Better serving and more authoritative hitting with the forehand earn Muguruza a hold to 15 - her first service hold of the match. 

We know Muguruza possesses formidable power, but she does have a Plan B? Halep is beating her up today, and Muguruza has no answer. One option would be to take a step back and avoid being rushed from the baseline, but at the moment it's more of the same. Halep holds to 15, helped on her way by a tremendous forehand winner crosscourt. She is absolutely purring right now. 

Muguruza is looking around the court bewildered by what is happening out there, disbelieving after a forehand zips past her for 30-30. It's reminiscent of the beating she dished out to Sharapova yesterday. Muguruza does work her way to a game point at 40-30, but she hastily bashes a backhand into the net with the court gaping. Halep makes her pay, earning a set point with some heavy backhand hitting and then taking it with a guided forehand winner up the line. 

Halep a set to the good after 37 minutes. Brutal stuff so far. 

At last Muguruza gets her side of the scoreboard moving. She breaks to 30, helped by a Halep double fault and a couple of unforced errors. 

Halep's really gone on the offensive over the last game or so, capitalising on the early momentum she's generated. A pair of brilliant forehand winners that paint the lines take Halep to 0-30. It should actually then be 0-40 - according to Hawk-Eye anyway - but a Halep forehand is adjudged to be just out, and it's 15-30 instead. Halep doesn't seem unduly bothered by the misfortune, earning another break point with some excellent defence. Muguruza  saves it, but Halep earns another one moments later - and this time she takes it as some more aggressive hitting forces her opponent to push a backhand well long. 

Halep will serve for a bagel set. 

Muguruza just can't find her range at the moment, and after slapping a couple of errors is on the receiving end of an ace as Halep wraps up a hold to 30.  

Halep scampers around the baseline keeping the point alive, and she eventually draws a netted Muguruza forehand for 15-30. Halep then finds good length from the baseline to earn another break point at 30-40, which she takes when Muguruza drags a forehand wide. 

This match has a bit of a Federer-Djokovic feel, with Muguruza consistently battering away trying to breach Halep's defences.  

A double-break lead should be enough for Halep this set. 

Muguruza's all-or-nothing game will mean errors like in the last game, but it also means there will be times when she takes Halep's racket away from her. A couple of bullet forehands move Muguruza to 0-30, and a third pummeled forehand brings up two break points at 15-40. But then there are the errors again, as Muguruza misses two makeable returns off pretty flimsy second serves. A third break point then comes and goes, as Muguruza pushes a backhand long. Halep eventually holds after a couple more missed Muguruza forehands. Big hold. 

As we expected, it looks like being a case of attack v defence today. Curently defence is winning. 

Two forehand errors from Muguruza have us at 0-30, before a mistake on the backhand side presents Halep with a break point at 30-40. A weak double fault hands over the break, and the world No. 1 has got off to the ideal start. 

Muguruza will serve first. We're under way...

It's a lovely, warm afternoon in Paris. I've just realised that judging by the tournament so far since everyone is saying how close this will be, it will probably be a thrashing. 

Chrissie Evert and Kim Clijsters struggling to pick a winner for this one. I fancy Muguruza to win in three, but it looks like being such an even match. 

The players will be on court in about half an hour. In the meantime, have a listen to the Tennis Podcast's look ahead to today's match. 

Not only is a French Open final on the line this afternoon, but the winner today will also claim the world No. 1 ranking. Simona Halep, the current incumbent, has never won a grand slam, while her opponent Garbine Muguruza won Wimbledon last year to add to her 2016 Roland Garros title. 

In short, this is proper, pressure second-week of a grand slam tennis. It should be a lot of fun. 

Muguruza is to my mind the slight favourite given her thumping 6-2, 6-1 win over Maria Sharapova yesterday, and greater pedigree at the majors. Halep was impressive in digging out a three-set victory over Angelique Kerber on Wednesday, but it was the sort of match-up she favours. Against Muguruza, there is the risk of her getting blown off the court by her opponent's power - see last year's final against the feraless and relentlessly aggressive Jelena Ostapenko. 

As great a mover and defender as Halep is, she could be left powerless if Muguruza is at her imposing best. Halep will also have to contend with the fact that once she makes it to the second week of slams, Muguruza comes alive. 

Often terrible in the first week and knocked out early, Muguruza is like the star Sunday League striker who will stay in bed for mundane early-season matches but then rock up for the cup final 10 minutes before kick-off and bang in a hat-trick. She is a big, big-time player. 

Muguruza also leads the head to head 3-1, including a 6-0, 6-1 shellacking of Halep in the Cincinnati final last year in their previous meeting. 

Halep is a different proposition on clay, but I'm still expecting Muguruza to get the job done today - in three sets. 

The players will be on court at 2pm, and the winner will play either Sloane Stephens or Madison Keys in Saturday's final.