Rafael Nadal beats Stefanos Tsitsipas 6-2 6-4 6-0 to reach Sunday's final
2009 winner Nadal will bid for second Australian Open title
Novak Djokovic and Lucas Pouille semi-final on Friday
Naomi Osaka beats Karolina Pliskova to reach Saturday's women's final
Osaka will face Petra Kvitova after Czech defeated Danielle Collins
Jonathan Jurejko
BBC Sport at Melbourne Park
Cheers as the tournament referee strides on to court... looks like we've hit five on the heat stress scale.
"According to the tournament heat policy we are now going to close the roof," says umpire Carlos Ramos.
More cheers and applause. The crowd clearly are hoping for some indoor ventilation...
*Kvitova 4-4 Collins
This is for tennis stadium roof fans - they are going to close the roof.
How exciting, eh?
Collins has left the court because it'll take two to three mins.
*Kvitova 4-4 Collins
Collins, no doubt spurred by the A-listers, holds.
Kvitova 4-3 Collins*
Image source, ReutersCollinss first serve just landed on the baseline - she recovers to produce a cracking forehand winner down the line.
Another big serve is too good for Kvitova.
30-0.
By the way, Aussie actor Nicole Kidman and her singing fella Keith Urban are inside Rod Laver's gaff.
Jonathan Jurejko
BBC Sport at Melbourne Park
Both players look to be coping fine with the Melbourne heat in the early stages.
As one of my media colleagues points out, these players are used to playing in heat all over the world on the WTA Tour.
Collins, being a Florida native, looks untroubled so far, so does Kvitova - although the Czech is grabbing her towel after every other point to mop her face.
Kvitova 4-3 Collins*
Now it's Collins' turn to scream after she digs out a Kvitova shot with the perfect backhand which drops just beyond her opponent.
40-30.
However, Kvitova manages to hold.
*Kvitova 3-3 Collins
Image source, Getty ImagesMaybe screaming/yelling helps.
Kvitova is starting to play like Kvitova.
A flat forehand brings up 40-0.
No love game though as she produces a double fault.
Jonathan Jurejko
BBC Sport at Melbourne Park
Image source, BBC SportThe Australian Open has introduced a new extreme heat policy, with a heat stress scale telling us how safe the players are in the conditions.
As I left the media centre, the heat stress reading was 3.9... and rising.
If it gets to four, which it surely will and actually might already have, then the players are allowed a 10-minute break between the second and third sets.
If a five is recorded, the tournament referee can decide to close the roof here on Laver and suspend the start of matches on outside courts.
*Kvitova 3-3 Collins
Break point five?
Yes, please.
Can she convert now?
Yes, with a forehand return past the reach of Collins.
That was slightly unexpected because Collins had started like a steam train and Kvitova had started like a toy train.
Kvitova 2-3 Collins*
Another break point and another scream from Kvitova.
Can she convert?
No, as Collins fires down the first ace of the match.
Bravo.
Deuce numero tres.
Kvitova 2-3 Collins*
Kvitova earns another break point after Collins finds the net.
The 28-year-old produces a scream of delight.
Advantage.
But she then makes her 12th unforced error by going long.
No screams.
Kvitova 2-3 Collins*
Kvitova goes wide from the back.
One saved.
30-40.
The Czech player then loops a return very long from Collins' second serve.
That was poor.
Deuce.
Jonathan Jurejko
BBC Sport at Melbourne Park
There are more fans wafting in those sun-drenched seats than there are at a Spanish Flamenco convention.
My arm is aching watching them waft.
Kvitova 2-3 Collins*
Is Collins getting a little too excited?
She attempts a sliced drop, but the ball fails to find its way over the net?
15-30.
Kvitova then strikes a forehand return past her opponent.
Two break-back points.
Kvitova 2-3 Collins*
Win Predictor - do you still think Collins has a 9% chance of winning this match?
15-15.
Jonathan Jurejko
BBC Sport at Melbourne Park
"Oooooh! What a shot!" exclaims one woman to the left of the media seats.
That double-backhanded return from Danielle Collins surprised the Laver crowd, popping off her racquet and dipping quicker than a Cristiano Ronaldo free-kick to find safety.
I dare say it might have even surprised her...
Kvitova 2-3 Collins*
One saved as Collins fires into the net.
30-40.
Collins breaks as Kvitova races wide but fails to loop her shot back into play.
What a start for the American!
*Kvitova 2-2 Collins
15-30.
Errors starting to creep into Kvitova's game.
The Czech then goes very wide with a forehand crosscourt return.
Two break points!
*Kvitova 2-2 Collins
Kvitova's shot is ruled out but she challenges - computer says "it was out".
So that is that.
All square.
Kvitova 2-1 Collins*
The 28-year-old then slightly tarnishes her good work by putting on too much meat on her forehand.
40-15.
Double fault. Collins' second.
40-30.