Muguruza comes storming into the net to reach a Williams drop shot and she executes the winner.

But the Spaniard fumbles with a couple of unforced errors as Williams levels for 30-all. 

But a special, special backhand down the line earns Muguruza break point and she overpowers the world number one to take the game. 

The fourth seed will now serve for the set. 

Image source, AP

Muguruza is serving to stay in the set now.

The 22-year-old pelts the ball past Williams for the opening point and then sees the American's forehand go way out wide.

But quick like a cat Williams returns a powerful Muguruza serve into the corner.

The Spaniard wrong-foots her opponent to move to 40-15 and she then levels the set again. 

A close one, this. 

What an ace from Serena Williams! Anyone fancy trying to return an 118mph serve? No, nor me. 

She double faults to bring the score to 30-all but makes up for it with a beautiful forehand winner.

And the world number one sees out the game to take a 5-4 lead. 

Image source, EPA

Jana Novotna
Former Wimbledon champion on BBC Radio 5 live

"It was very clever, patient play from Serena Williams. She put up two high balls, completely changed the pace, and really disrupted Muguruza's timing on the last ball."

An ear-splitting scream erupts from the vocal chords of Serena Williams as she misses a forehand return. I think she's deafened the front row on Philippe-Chatrier Court.

For the second time in the game, Garbine Muguruza finds her shot in the net. 30-30.

Williams' forehand deceives the Spaniard to earn break point and she levels the set after Muguruza hits long. 

Parity is restored.

Image source, Reuters

Williams shows some respect to Muguruza as she claps a fabulous forehand winner down the line. 

From here, the American sees out her service game. But she now needs to think about a break. 

Russell Fuller
BBC tennis correspondent in Paris

"The story of this match so far is very hard hitting from the baseline. The players look like they are trying to hit seven bells out of every single ball they face."

Hummm, there's a case of double fault-itus (it's a thing). Muguruza gifts Williams the opening two points with some dodgy serving.

Muguruza draws level at 30-all and finally we enter a couple of rallies. Powerful ones at that.

It's Muguruza who comes out on top by slamming a forehand winner tight into the corner to take the game. 

Image source, AP

Jana Novotna
Former Wimbledon champion on BBC Radio 5 live

"We sometimes say, 'Don't break, and get broken' - Serena had a couple of opportunities to break in the last game and then she lost her own serve in the next game. Very gutsy play from Muguruza, hitting that backhand return from the baseline."

That last game seems to have fired up Garbine Muguruza - she earns triple break point.

Williams smashes an unstoppable ace to save one, and saves another after Muguruza fails to return a heavy second serve. 

But it's first blood to the Spaniard - she takes the game after a double fault from the world number one. 

Image source, AP

Jana Novotna
Former Wimbledon champion on BBC Radio 5 live

"We knew that we wouldn't see too many long rallies. But so far you have to admit that the hard-hitting and heavy serving from both players is impressive."

Image source, Getty Images

KJ Poulton: Will the women's final last more than an hour?

Lewis J815: Please not another Williams win! Share the wealth... Either way, let's see three sets!

Muguruza has another advantage, after Williams' backhand is smashed long, and after nearly 10 minutes of trying, the Spaniard finally holds - fending off two breaks from her opponent. 

Williams accelerates into the net and volleys past Muguruza to take the advantage, and a second break point.

But it's rescued again by the Spaniard, who smashes a quality ace down the middle. That's the way to do it!

Muguruza then takes the advantage after a failed Williams drop shot, but she can only swipe into the net to take us back to deuce again. 

The fourth seed has another advantage...but a double fault brings us to deuce number four. 

Another blistering serve from Garbine Muguruza which Serena Williams fails to return. The Spaniard really gets her weight behind them.

Williams hits long on the next point but then manages to out-wit her opponent with a drop shot that Muguruza snatches at.

And then the  fourth seed smacks into the net to make it 30-30. 

Williams places a near-perfect forehand into the corner to earn break point, but it's saved by Muguruza. We go to deuce.

Image source, Getty Images

Serena Williams looks far more comfortable in the early stages of this match than she did in her semi-final against Kiki Bertens. 

It looks like she's shaken off the thigh injury which was troubling her.

The world number one sees out her service game with no drama. 

Image source, Getty Images

A strong serve, which surpasses 100mph, sees fourth seed Muguruza move to 30-15. 

She follows it up with another powerful second serve which evades Williams.

The American does snatch a backhand winner, but then hits into the net on the next point.

Muguruza holds. 

Russell Fuller
BBC tennis correspondent in Paris

"It was interesting that Muguruza won the toss and asked Williams to serve, no doubt remembering what happened in the Wimbledon final last year, where Serena served three double-faults in her opening service game. But that, in stark contrast, was a cracking service game."

On her second serve, Williams claims the first point after Muguruza flies a backhand past the baseline.

And then the Spaniard puts a forehand into the net.

Williams lands a blistering ace for 40-0 and lands another strong serve to hold to love. 

Here we go, then. From 128 we've got it down to two.

Serena Williams, defending champion, will get us underway in the French Open women's singles final. 

Image source, Getty Images