Victory in Monday's clash between Group B's hitherto unbeaten duo put them in charge of the section with the knowledge they can all-but secure a last-four spot with a decent win over Scotland on Sunday.
Australia will have watched England's successful spinners and solid upper-order batting with interest. Victory over New Zealand at the same Sharjah venue on Tuesday (Wednesday 0100 AEDT) will put them in control of Group A increasing the likelihood the Ashes rivals will avoid each other in the semi-finals.
Set 125 to win England always looked favourites and ultimately clinched victory with four balls to spare, the chase based on a 64-run 55-ball third-wicket partnership between Danni Wyatt-Hodge (a run-a-ball 43) and Nat Sciver-Brunt (48 not out off 36).
The win partially avenged successive defeats on this stage against the Proteas, including in last year's semi-final.
Opting to bat first South Africa began and ended well but became bogged down mid-innings. After the six-over opening powerplay they were 1-37, the last five overs went for 39, the best death batting of the event to date. But in the nine overs in-between they scored 48 .
Captain Laura Wolvaardt anchored the innings scoring 42 off 39 balls while Marizanne Kapp (26 off 17) and Annerie Dercksen (20 off 11) provided late impetus.
England's Sophie Ecclestone is congratulated by Dani Gibson on taking the wicket of Marizanne Kapp. (AP PHOTO)
But Kapp and Wolvaardt were both dismissed by Sarah Ecclestone, who lived up to her billing as the No.1 bowler in the women's game.
"Two big wickets, I was happy to get them out," said Ecclestone whose 2-15 off four overs was well supported by fellow spinners Sarah Glenn (1-18) and Charlie Dean (1-25).
"I'm really pleased. I thought it would be a tricky chase but we controlled it brilliantly, that partnership was outstanding to watch," England captain Heather Knight said.
England were 1-28 after the powerplay as they struggled to get Kapp away and by the mid-point were 2-55, still needing 70. But after Wyatt-Hodge and Sciver-Brunt got the rate to a run-a-ball with five overs to go they eased to victory.
While Knight was pleased with England's energy in the field catching remains an issue with four sharp chances missed plus a run-out.
Dropped catches have been a theme of the tournament, which some have suggested is due to the placement of the floodlights (though day games have also featured catches going down).
Apart from missing Wolvaardt on 22 England's butterfingers were not too expensive. Not so South Africa's. Alice Capsey, dropped on nought, went on to make 19. Wyatt-Hodge was then missed on 31 and 37 at a stage when South Africa badly needed a breakthrough.
"We're obviously very disappointed," Wolvaardt said. "We were talking 140-mark and 10-20 more runs with the bat could have made it interesting but we lost our way for a period and didn't take our chances in the field."
2°C