Dean stars with four wickets; Wong takes three wickets on debut
Dunkley hits her first ODI century - off 87 balls
Lamb and Beaumont put on 127 for first wicket
England now lead multi-format series 6-2
Highlights on BBC iPlayer from 07:00 BST on Saturday
Beaumont c Ismail b Tryon 58 (Eng 147-2)
Well, I've just jinxed it for Tammy Beaumont.
Sorry.
Beaumont attempted to loft the ball over mid-off but doesn't get enough on it and the ball is safely pouched by Shabnim Ismail.
A fine innings from the England opener though.
Image source, Getty ImagesThanks, Ffion.
So far, so good for England. I think they could go big here.
Henry Moeran
BBC Test Match Special
Tammy Beaumont's fingers have cramped up! She's taken her glove off and has given them a stretch! Utterly bizarre!
Oh, how has that missed?!
Mlaba darts one in that Dunkley edges just past her stumps, and South Africa gasp at the agonising closeness.
Meanwhile keeper Trisha Chetty is helping Tammy Beaumont with some cramp in her fingers. What a strange sight!
Anyway, Beaumont makes a full recovery and it's time for me to have a breather and hand over to Tom Mallows to take you through the rest of England's innings.
Georgia Elwiss
England all-rounder on BBC Test Match Special
There's no urgency or buzz from South Africa. Then when an opportunity does come, they are not taking it.
They need someone to step up.
Shabnim Ismail shows some of the fight and determination that South Africa need as she sprints back from mid-off to save a boundary. A brilliant piece of work.
If some of the others could match her enthusiasm, that'd make a big difference.
Georgia Elwiss
England all-rounder on BBC Test Match Special
Beaumont and Dunkley are going really nicely. There are plenty of runs on offer out there. Both of these players will be hungry to score runs and that is what England will need to get over 300.
So, Tammy Beaumont has been given a life and that drop just sums up where South Africa have been so far.
Halfway through and England are in an excellent position to kick on.
Melissa Story
BBC Test Match Special
It was a nice catching height. That's a bad drop there. She should be taking that wicket. Massive missed opportunity for South Africa.
Oh, that is poor.
Marizanne Kapp has had a tough day but she finally gets a chance, Beaumont playing a false shot straight to mid-on where Nonkululeko Mlaba drops it.
It was hit hard but she got two hands to it. That should've been taken. You don't want to give Tammy Beaumont a life.
Treat yourselves to the best bits of Emma Lamb's second successive half-century in an England shirt.
Alex Hartley
Former England bowler on BBC Test Match Special
If you do tweet in, and you aren't backing me, you better be prepared to tell me why!
#bbccricket or text 81111 (UK only - standard message rates apply)
Melissa Story
BBC Test Match Special
Tell us who you think would win the mascot race out of the TMS group!
A good tight couple of overs from South Africa here.
Can England see it out?
Alex Hartley
Former England bowler on BBC Test Match Special
Lauren Winfield-Hill is such an athlete. She'd beat us all, hands down!
Melissa Story
BBC Test Match Special
If we all got dressed up in a mascot race, who are you backing to win Alex?
Beaumont 51, Dunkley 2
Marizanne Kapp returns in an attempt for South Africa to put some pressure on the new batter.
Just two runs from the over.
TMS are currently talking about mascot races. I wouldn't want to be in one of those outfits at Finals Day tomorrow. Imagine how sweaty it'd be.
Sophia Dunkley is the new batter and she sees off the rest of Chloe Tryon's over calmly.
Alex Hartley
Former England bowler on BBC Test Match Special
Another fine fine performance for Emma Lamb who looks so comfortable in an England shirt.
Melissa Story
BBC Test Match Special
Image source, Getty ImagesEmma Lamb goes via the softest of dismissals. She looks visibly disappointed. It couldn't have gone any worse for her. Finally South Africa have a breakthrough.