Why didn't you try to lob her Rybarikova as she came to the net?

Anyway, an ace pulls her level.

Error number 400 = 15-30.

Ace. 30-30.

Here's something. Rybarikova wins yet another long rally as she forces Muguruza to fire a return into the net.

Continue that tactic Mags?

She tries, but Garbs moves into the net once more and the pressure again is too much for her.

Deuce becomes advantage Muguruza.

The Spaniard takes the break with another sortie to the net.

Jonathan Jurejko
BBC Sport at Wimbledon

"Come on Maggie!" shouts a lad in front of the press seats. He gets an elbow from his female companion for his troubles.

"Sssh. You're so embarrassing" she tells him.

But the point is he's trying to encourage the Slovakian world number 87. She's struggling, as the scoreboard clearly shows, with the pressure of her first Grand Slam semi-final.

Rybarikova has form on grass, but can she find it today before it's too late?

Tracy Austin
Former Wimbledon mixed doubles champion on BBC Radio 5 live

The body language of Rybarikova is so different today.

She is negative with her hands and facial expressions and is looking up to her support box.

0-30 on the Muguruza serve.

Hmm, let's not get carried away though.

And rightly so, it's 15-30 ...and now 30-30 after Rybarikova applies too much juice on a forehand as she went for the kill.

That's followed by another shot from Mags that fails to climb the net.

It's set point for Muguruza.

That becomes "first set Muguruza" as Rybarikova's wayward backhand slice is... wayward.

She needs a Rocky-style stool talk.

Image source, PA

John McEnroe
Three-time Wimbledon singles champion on BBC TV

The mercy applause is slightly painful but you will take all you can get...

They're just 15,000 people on Centre Court in the commentary - no pressure Rybarikova. Plus a few million watching and all that...

Probably her best points so far to take it to 15-15 - she stays in the point on a rally and forces an error from Muguruza.

And then a sign? After evil net cord doesn't go here way she attempts a keepy-uppy with the ball which goes wrong. She performed one brilliantly against Vandeweghe the other day.

But the poor footwork doesn't upset her. She holds with a big serve.

Where there is no bagel, there is hope, as someone never said.

Image source, Getty Images

Jonathan Hextall: Wow this is the Muguruza we've been waiting for.

Bridgette Parlma: Garbi toooo good.

Lee Fergusson: A brilliant start to this match by Muguruza!!

Jonathan Jurejko
BBC Sport at Wimbledon

Hearty applause greets every point won by Magdalena Rybarikova. Centre Court wants a contest.

Kim Clijsters
Former world number one on BBC TV

Rybarikova looks a little overwhelmed. I am even wondering if it will go away. It might if she wins a game but at the moment the stress is still there.

15-30 to Rybarikova - break back time?

Nope. She sends another forehand down the wrong line.

But wait - she does have break point. This is it Magdalena - your big moment.

Alas, Muguruza once again comes to the net and despatches a shot that lands in the no-man's land near the feet. Un-pick-up-able.

Deuce before Muguruza serves an ace to hold.

The bagel is almost fully baked.

One-way traffic so far in this first set, Muguruza dominating with shots like this.

John McEnroe
Three-time Wimbledon singles champion on BBC TV

When you are nervous, your legs aren't working, you can't seem to move well, you feel heavy, nothing is working.

It's a horrible feeling.

Advantage Muguruza, who again wrong-foots her opponent, before the Spanish world number 15 forces an error from Rybarikova who was looking for the big winner down the line but instead chose the wrong line.

It is now 4-0.

Image source, Reuters

The thing is Rybarikova had a very easy ride in her last match against CoCo Vandeweghe who was, to be blunt, a shambles. Here, she is actually being tested.

Muguruza is moving freely despite the strapping. She swings her opponent from side to side on the second point. 30-0.

She then comes to the net and plays a good enough volley to give herself three break points.

This is 4-0 surely. No. Rybarikova bites back and saves all three.

Deuce.

Advantage Muguruza after she comes to the net.

Deuce after Rybarikova does the same.

More to follow...

Image source, EPA

Mary Pierce
Former French Open champion on BBC Radio 5 live

Rybarikova looks tense in her face. You can see she has not settled into this match.

Tracy Austin
Former Wimbledon mixed doubles champion on BBC Radio 5 live

Muguruza has only been broken four times on the way to the semi-finals. She has a good service motion and hits her areas well.

Rybarikova is having a bit of a 'mare at the moment.

It's 40-0 and she appears to half-heartedly challenge on the next point as she heads to her seat - but no, Hawk-Eye hands her a reprieve. Back to the baseline for you, there's more of this third game to play.

She doesn't make the most of it - 40-15 becomes game Muguruza after the ball comes off the frame of her racquet.

Could it be bagel o'clock?

Kim Clijsters
Former world number one on BBC TV

Muguruza is a superb athlete. I think the strapped leg is more for injury prevention so I think we will see some of her great movement out there.