England beat the Proteas by six wickets in the first women’s T20I at the County Ground in Chelmsford on Thursday.
The hosts also secured a multi-format series win, with an unassailable lead of 10 points to two.
Katherine Brunt led England’s charge with the ball, picking up her first T20I four-wicket haul to help restrict South Africa to 111-9 despite Laura Wolvaardt’s 55 off 49 balls.
Opening batter Sophia Dunkley then scored a maiden half-century (59 off 39 balls) as England reached their target with five overs to spare.
The second T20I is on Saturday (15:30) at New Road in Worcester.