Eng 72-0published at 10.2 overs
Slower ball from Khaka but it's too full, very wide and Lamb stretches to reach it and loft the ball over extra cover for four.
After a slow start, she is starting to motor now.
Summary
England win by 109 runs
SA 262 all out: Tryon (70), Kapp (62), Wolvaardt (56); Davidson-Richards 3-35, Dean 3-42, Lamb 3-42
Eng 371-7: Beaumont 119 (107), Lamb 65 (66), Knight 63 (49); Khaka 2-64
England lead multi-format series 8-2 before three T20s
Use audio icon at top of page to listen to BBC Radio 5 Live Sports Extra commentary
Watch highlights on iPlayer from 07:00 BST on Tuesday
Eng 72-0published at 10.2 overs
Postpublished at 14:48 British Summer Time 18 July 2022
Anya Shrubsole
Former England bowler on BBC Test Match SpecialIt is a very good pitch but South Africa can still contain the scoring by just bowling straight.
We can complicate cricket so much with plans and match-ups, but actually if you just bowl at the stumps that's the best way to go.
Eng 66-0published at 10 overs
Lamb 23, Beaumont 30
The extras just keeping coming. Nadine de Klerk oversteps with what should have been her last ball - although it would have been called wide if it wasn't a no-ball.
Lamb makes the most of this one, clubbing the ball over mid-on for a one-bounce four. It's all looking good for England so far.
Postpublished at 14:45 British Summer Time 18 July 2022
Anya Shrubsole
Former England bowler on BBC Test Match SpecialTammy Beaumont plays at her best when she has got a point to prove.
Eng 60-0published at 9.3 overs
Last over of the powerplay and Beaumont is cashing in. Short from De Klerk and it is pulled authoritatively through mid-wicket by the England opener.
It's been a super start for the home side.
Postpublished at 14:43 British Summer Time 18 July 2022
Anya Shrubsole
Former England bowler on BBC Test Match SpecialIt already feels like it's going to be a very long day for South Africa.
Eng 53-0published at 9 overs
Khaka may be a little fortunate not to be called for a no-ball for height as she sends down a high full toss to end the over.
It was marginal but the umpires give the bowler the benefit so it is just a single for Lamb, no free hit for Beaumont.
Postpublished at 14:42 British Summer Time 18 July 2022
Alex Hartley
Former England bowler on BBC Test Match SpecialEmma Lamb looks like she really belongs in international cricket.
There was a lot of talk about the fact she should've been in the side sooner but I think they've got the timing just right because she's confident now and knows her game well.
Eng 52-0published at 8.4 overs
Lamb 16, Beaumont 24
Make that two fours for Lamb - and this one is far more convincing. She plants her front foot forward and launches the ball over mid-on, a couple of bounces and it's over the rope.
Lovely shot.
Postpublished at 14:40 British Summer Time 18 July 2022
Just one boundary for Emma Lamb so far, it came via a thick outside edge off Marizanne Kapp.
Postpublished at 14:39 British Summer Time 18 July 2022
Anya Shrubsole
Former England bowler on BBC Test Match SpecialThat over sums up South Africa's ODI series so far.
They build pressure and then release it at the last second. It should've been a single, but instead it's four and that turns it into another good over for England.
Eng 45-0published at 8 overs
More sloppiness from South Africa, this time from the seventh ball of Nadine de Klerk's first over after an earlier legside wide.
Beaumont hit it firmly to mid-on but it should have been stopped. Instead, it ricocheted off the fielder and races away for four.
Postpublished at 14:33 British Summer Time 18 July 2022
Anya Shrubsole
Former England bowler on BBC Test Match SpecialIt's been a really good start, just what England needed. South Africa have got to bowl straighter otherwise they'll be chasing another big score.
Postpublished at 14:33 British Summer Time 18 July 2022
Speaking of those boundary balls, here is the first of them from Ismail - pulled away in front of square by Tammy Beaumont.
Postpublished at 14:32 British Summer Time 18 July 2022
Alex Hartley
Former England bowler on BBC Test Match SpecialAyabonga Khaka started really well but you could tell that Tammy Beaumont was just waiting for the loose ball. She knows it's coming, so she doesn't mind having to defend a few balls first.
Eng 40-0published at 7 overs
Khaka starts with a good ball, that just nips away from a good length to beat Beaumont.
However, in fitting with the innings so far, a loose delivery is not far behind and Beaumont crashes a drive through the covers for four more.
Postpublished at 14:30 British Summer Time 18 July 2022
Change of bowling for South Africa, Ayabonga Khaka is on with the chance to mark her 30th birthday with a wicket or two.
Postpublished at 14:29 British Summer Time 18 July 2022
Alex Hartley
Former England bowler on BBC Test Match SpecialI'd say I've pulled a hamstring.
Postpublished at 14:29 British Summer Time 18 July 2022
Emily Windsor
Southern Vipers batter on BBC Test Match SpecialIf my captain told me we'd won the toss and chosen to bowl in these conditions, I would not be happy.
Eng 35-0published at 6 overs
Much better over from Kapp. She produces a beauty that snakes past Lamb's outside edge before the England opener nails a drive straight to the fielder at cover.
Another good ball follows, Lamb pushes at it and gets an edge... well wide of the only slip and it bobbles away for four.