Debutant Ryana MacDonald-Gay's first Test wickets either side of a lightning stoppage sparked a middle-order collapse as England hammered home their advantage on day two of their one-off match against South Africa in Bloemfontein.
Marizanne Kapp's 57 off 74 balls - the third-fastest half-century by a South African woman - led the Proteas fightback in response to England's first innings total of 395-9 declared before MacDonald-Gay removed her off stump to claim her first Test match wicket.
The umpires took the players off the field after lightning strikes close to the Mangaung Oval, but after the 50-minute delay, 20-year-old MacDonald-Gay removed Nadine de Klerk for nought to swing the momentum firmly back towards the tourists.
South Africa were 237-3 at one stage after captain Laura Wolvaardt scored 65 and a 99-run fourth-wicket stand between Kapp and the gutsy Sune Luus.
But the hosts capitulated after MacDonald-Gay's exploits, losing seven wickets for 44 runs as Lauren Bell (4-49) and Lauren Filer (2-53) wreaked havoc with the new ball, bowling South Africa out for 281 runs, 114 short of England's first-innings total.
Captain Heather Knight (19no) and Tammy Beaumont (8no) saw England through to stumps on 31-1, the dismissal of first-innings centurion Maia Bouchier the only blot after an impressive day in the field for the tourists, who have a 145-run lead and victory in sight heading into day three.
Having failed to remove either South African opener in six, tense overs at the end of the opening day England struck gold in the second over on day two, Bell coaxing Anneke Bosch into a shot she didn't need to play as a faint outside edge carried through to wicketkeeper Amy Jones.
That saw Annerie Dercksen join Wolvaardt in the middle and their partnership frustrated England, Wolvaardt's 99-ball half-century leading the South African response as the pair put on 92 in the morning session.
Dercksen looked on course to follow Wolvaardt through to a half-century after being dropped by Bell at deep fine leg while on 33 but she was only able to add eight to her total, Filer striking in the final over before lunch.
A venomous delivery nipped up off Dercksen's bat before being caught on the rebound one-handed by Sophie Ecclestone after it was parried into her path by captain Knight at second slip.
With South Africa resuming 282 runs behind after lunch, the onus was on Wolvaardt to replicate her exploits in Chennai on her last Test outing and convert her half-century to three figures, but she would last just nine overs into the afternoon session.
Adjudged to have been trapped lbw in the second over of Ecclestone's second spell on 65, with DRS not in use to review her claim there was an inside edge, the South Africa captain cut a frustrated figure as she trudged back to the pavilion.
A gutsy knock from Luus saw her add 47 runs but it was Kapp's blistering 48 off 58 balls - at twice the pace of Luus - which left South Africa in the ascendancy, as an 87-run fourth-wicket stand left the hosts 170 runs behind at tea.
Kapp and Luus clinched their half-centuries within three overs of each other but the partnership was undone a run before reaching three figures as a superb MacDonald-Gay delivery straightened to remove Kapp's off stump.
Lightning strikes and storm clouds forced the players from the field and covers to be drawn but, with no rain falling on the ground, play resumed within the hour, MacDonald-Gay striking again in her first over to remove De Klerk for a duck.
With the new ball just two overs old, the dangerous Luus was removed and from there South Africa crumbled as seamers Bell and Filer ripped through the middle-order and tail with little resistance, Bell removing Sinalo Jafta and Nonkululeko Mlaba in two balls to finish with figures of 4-49.
Ayanda Hlubi's dismissal of Bouchier for nought provided a small crumb of comfort for South Africa but Knight and Beaumont's diligence at the crease through to close ensured England remain firmly in the box seat.
Speaking to the BBC after the close of play, Lauren Bell said: "It's been a great day. We'd definitely have taken that at the start. They had patches where they made good partnerships. We're really happy.
"It's the Kookaburra [ball] so it doesn't swing for ages up top. It's not massively different. It's just trying to repeat as much as possible. It's been really fun to be out there with the girls.
"Missing Kate Cross is a massive loss but our roles stayed pretty similar. We wanted to stick to our strengths. My job up front is to swing the ball and take wickets with the new ball. Filer bowls fast and she was unbelievable today.
"The pitch is giving us movement without having to do a lot. It's nipping and the wobble ball is wobbling. We're not having to do loads because the pitch is helping us out a lot."
Watch day two of the one-off Test between South Africa and England live on Sky Sports Cricket from 7.40am on Tuesday (8am first ball). Coverage is also on Sky Sports Main Event from 8am.
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