Even the net cords are going Halep's way, as she loosely slashes at a forehand, and the ball just drops over.

That's a gorgeous backhand from Halep to the serve, and she cracks yet another winner to give herself three break points.

Glorious winner from Simona Halep, spinning her forehand down the line. She looks in total control.

Down comes the ace, and just like that, Halep holds to love. She's only dropped three points in the match so far.

It was Karolina Pliskova who raced to a 3-0 lead in the quarter-final against Simona Halep.

The boot is firmly on the other foot today.

Piers Newbery
BBC Sport at Melbourne Park

The mid-match refuelling is well under way around the grounds at Melbourne Park, but we're probably two-thirds full for the start of this one.

It's 29C in the stands so probably a fair bit warmer down on court, but fitness is not likely to be an issue with these two women - you will do well to find much more highly-tuned athletes anywhere.

Halep did roll her ankle badly in her first-round match, and there was some speculation that she might not even make it out for round two, but the Romanian has looked as tough as teak ever since.

Image source, BBC Sport

Seven minutes on the board, and Simona Halep is a double break up!

It's not clicking for Kerber, as she hits a backhand on the move and slices it well out of bounds.

Ooh! Kerber comes forward, gets into the perfect position for the smash - and it just about gets over the net, with a bit of help from the tape! She raises her hand in apology.

Dearie me. This isn't going well for Kerber, as she sends a drop shot straight into the net. Two break points again for Halep!

Outrageous angles from Halep as she's pushed wide by Kerber, and it's Kerber who blinks first as she shanks a forehand into the net.

Kerber gets a point with a fine forehand winner off a Halep serve, but it's the only one she manages as Halep holds with a good body serve.

There is the break!

Her second serve is a little weak, and Halep's response draws the error out of Kerber.

Simona Halep is wearing an Australian Open-branded visor, because she's currently without a clothing sponsor. Remarkable, considering she's world number one.

The first point goes Angelique Kerber's way but a shimmy forward allows Halep to crack a backhand winner over.

Into the net goes Kerber, and Halep has two break points to start with.

Ready?

Angelique Kerber will serve to get things going.

Angelique Kerber captured the title in Melbourne in 2016, while this is Simona Halep's best run in Melbourne.

Simona Halep, by contrast, ended the year as world number one after a topsy-turvy season.

Halep reached the final of the French Open and looked set for her maiden Grand Slam victory, before she was stunned by Jelena Ostapenko.

She also temporarily lost her coach, Darren Cahill, after he was unhappy with her effort in a match.

Spurred on, Halep went on to defend her title in Madrid and looks, both mentally and physically, stronger than ever.

Image source, EPA

2017 was Angelique Kerber's annus horribilis - she lost her world number one ranking, failed to defend either of her Grand Slam titles and looked like the weight of the world was on her shoulders.

It's been a different story this year.

Backed by a new coach, Kerber is unbeaten in singles matches this year, and captured the title in Sydney earlier this month.

Her demolition of Madison Keys in the quarter-final highlighted just how hard she's worked to put last year behind her.

Image source, Reuters

Got the teas and the coffees in?

Ready for another semi-final? Excellent.

Image source, Getty Images

Who will be meeting Caroline Wozniacki in the final?

Up next it's Simona Halep v Angelique Kerber, which should be one heck of a match.

I'm off to stick the kettle on and find some snacks - do stick around, though, as play should begin in about 15 minutes time.

Image source, Getty Images

A reminder that, if Simona Halep loses in the semi-final up next, Wozniacki will become world number one.

If Halep beats Angelique Kerber, then it's a straight shoot-out in the final to take the crown.

Caroline Wozniacki has just apologised to her dad for the stress in that final set.

"My dad used to have black hair - now it's all grey because of me!"

Dad looks like he might see the funny side of this in about an hour's time.

Props to Elise Mertens, who showed quality today but just not quite enough.

It's her best run at a Grand Slam final, and it's been superb to see.

Your first Australian Open finalist, folks.

Caroline Wozniacki freely admits in her post-match interview that she had that 2011 semi-final on her mind. Massive, massive smile on her face.

Image source, EPA