SA (127-4) win with two balls to spare
Van Niekerk (46) & Kapp (38) share stand of 84
England post 123-8
Sciver makes half-century from 40 balls
Adds 32 with Brunt in three overs
England were champions in 2009 and three-time runners-up since
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Lee c Winfield b Shrubsole 4 (SA 6-1)
There's the wicket England needed. Lizelle Lee tries to run before she can walk, succeeding only in scooping Anya Shrubsole to mid-on. Big celebrations from England. They know they've started well here.
Nicky Shaw
Ex-England all-rounder on BBC Test Match Special
Katherine's been bowling cross-seam recently and not getting the shape away, which is her biggest weapon - so I had a word with her, and I hope she's bowling seam-up today.
Night has taken hold in Perth. The floodlights illuminate the famous old ground. Both of these right-handers are betting out of their crease in a bid to negate the swing, but Lee is still beaten by one that arcs away. Next one, straight, hit on the pads. Appeal turned down.
Nicky Shaw
Ex-England all-rounder on BBC Test Match Special
I'd like to see a slip in for Katherine Brunt - you always need to attack at the Waca. And it's nice to see Heather putting herself in at slip as there's every chance of an edge as Katherine moves the ball away, and Lizelle Lee goes hard at it.
Target 124
Just one more from the over. England will be encouraged by the movement - they need wickets if they are going to win this game. Katherine Brunt will share the new ball.
Henry Moeran
BBC Test Match Special
South Africa don't bat as deep as England, but in Lizelle Lee arguably have a player who is superior in terms of the 22 on the field - and can win you a game in double-quick time.
Target 124
Swing for Shrubsole, but Lee isn't fussed. She shows her intent with a loft down the ground for a couple.
Nicky Shaw
Ex-England all-rounder on BBC Test Match Special
It's a new England squad, with a new coach finding her feet, but there's a bit of muddled thinking about who bats where. This team hasn't won a T20 World Cup since 2009, so something had to change. They've got a lot of choices - I think Nat Sciver should be batting at three, she knows these grounds well, and I love Katherine Brunt coming in above Tammy Beaumont. But this England team hasn't got their head around it just yet.
Lizelle Lee marks her guard, with Dane van Niekerk at the other end. Anya Shrubsole has the ball.
Can England avoid being on the end of a shock?
Nicky Shaw
Ex-England all-rounder on BBC Test Match Special
After the start they got, 123 doesn't look too bad. South Africa rely on a few of their top order, like Lizelle Lee - I think England will be OK, they can defend 123 but they have to bowl well and have a good powerplay.
Where would they be without Nat Sciver?
Only five times before have England defended a total lower than this one to win a T20. The most recent was 119 in India last March. All the rest, though, were in 2012 or before.
Thanks, Mitch.
Now, can anyone please explain to me why Tammy Beaumont, the player of the tournament at the 2017 World Cup, is coming in at number seven with only 14 deliveries to go?
I'm going to hand you over to Stephan Shemilt to talk you through South Africa's reply...
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Danni Wyatt, Heather Knight and Fran Wilson then departed before Natalie Sciver's half-century led England's revival.
Alex Hartley
England spinner on BBC Test Match Special
It feels like I've been harsh on the England batters, but they've got the bowling attack to defend this. They need to be careful with their lines and lengths, and squeeze the South African batters.
Amy Lofthouse
BBC Sport at the Waca
Interesting that South Africa had a huddle before they left the pitch, with Dane van Niekerk leading the talk - they've never beaten England in a T20 World Cup...
To run through some highlights quickly - Amy Jones looked good with some early boundaries before falling for 23...
Alex Hartley
England spinner on BBC Test Match Special
England don't look to be firing. There is Beaumont and Winfield at seven and eight. It looks like England are playing too safe and not playing their natural games.