I think it's good bowling combined with batters perhaps a little uncertain on precisely how to approach the task in hand, Ozzy.

David Miller is way way too early on one from Pat Cummins and chips it up to mid-on. Josh Hazlewood is caught in two minds about whether to go for the catch or prevent the boundary.

He does neither and has to offer apologetic words to Cummins. Four runs.

Jonathan Agnew
BBC cricket correspondent on Test Match Special

A loosener from Cummins. Just a bit full and floaty and for once, South Africa find the gap.

A counter-attacking shot across the bows from Heinrich Klaasen as he drives the first ball from Pat Cummins through the covers for four.

He just leaned into that. A classy shot.

Liam: Klaasen may well be the best player of spin in the world but that won't really matter much if he runs out of partners.

Aaron Finch
Former Australia captain on BBC Test Match Special

I wasn't expecting to see this much assistance from the surface here. It is usually a ground where you can cash in during the powerplay.

It's the length from both bowlers that has been so consistent. I can't remember seeing a ball that has been there to drive.

Mitchell Starc continues as Pat Cummins goes for the jugular.

There's a few streaky singles as Heinrich Klaasen chips one just wide of cover while David Miller inside edges one down to fine leg.

South Africa need a few quiet overs here just to regain some compsure.

Jonathan Agnew
BBC cricket correspondent on Test Match Special

They are perfect bowling conditions but South Africa are nowhere. It feels like something could happen every ball.

South Africa's dominance batting first has been built on basically standing still and whacking it. That is now being challenged by a hint of movement.

Firdose Moonda
Cricinfo writer on BBC Test Match Special

It's not quite what we all expected when South Africa won the toss and chose to bat!

David Miller edges his first ball from Josh Hazlewood, but it races away through the slips for four. A huge let-off.

Aaron Finch
Former Australia captain on BBC Test Match Special

The perfect length from Josh Hazlewood again. It is the first time we have seen Rassie van der Dussen try and drive.

There isn't much movement, he's just pushing at it. No messing around from Australia.

Simon Mann
BBC Test Match Special commentator

South Africa are in tatters.

Aaron Finch
Former Australia captain on BBC Test Match Special

Heinrich Klaasen is one of the best players of spin in the world. He can dominate from ball one, so I think we'll see Cummins turn to Mitchell Marsh before he goes to Adam Zampa.

Simon Mann
BBC Test Match Special commentator

That is one of the most extraordinary powerplays. South Africa have tried to play their shots but they haven't been able to get any of them away.

And when they did get them away, Australia's fielding hasn't allowed them to reach the boundary.

David Warner is excitedly buzzing about like a fly around an open jar of jam.

Josh Hazlewood draws an edge from the bat of Heinrich Klaasen but it falls just short of second slip. Not let for the South African batters.

Simon Mann
BBC Test Match Special commentator

We knew South Africa would bat first if they won the toss, no matter what. But unfortunately they've had to do it on a day where it's cloudy and overcast, the only day we've seen with conditions like this in the entire tournament!

Aaron Finch
Former Australia captain on BBC Test Match Special

It's a hard drive from Markram and his eyes lit up because it's one of the only full balls that Starc has offered.

David Warner is never dropping that. It's a big wicket because Aiden Markram was looking to take the game on and put the pressure back on Australia.

It's miserable overcast and murky. Heinrich Klaasen is the new batter.

Josh Hazlewood is at the top of his mark.