England beat the Proteas by five wickets in the first women’s ODI in Northampton on Monday.
After winning the toss and opting to bat first, the visitors were bowled out for 218 in 47.4 overs, with Chloe Tryon scoring 88 off 73 balls and Laura Wolvaardt 43 off 72.
Nat Sciver was England’s best bowler, taking 4-59, before scoring 55 off 36 balls with the bat in their successful run chase.
Sciver was involved in an 89-run third-wicket partnership with opener Emma Lamb, who made 102 off 97 balls.
Nadine de Klerk, who made 38 with the bat, picked up two wickets for the Proteas.
England needed just 32.1 overs to reach their target and take a 1-0 lead in the three-match series.
The second ODI will take place in Bristol on Friday.