The home side has an unassailable 3-1 lead in the five-game T20 series.
The visitors will be doing fielding drills from now until oil prices return to normal, following a clumsy effort in the field.
They grassed four catches.
Sophie Devine was spared twice.
The veteran all-rounder was dropped on naught and again on 25.
She celebrated her good fortune by pummelling 64 from 34 balls in her 150th T20 international.
Ironically, she was dismissed by a wonderful catch by Nadine de Klerk.
But by then, the target was in sight. Brooke Halliday nudged the ball into the leg side to clinch victory with nine balls remaining.
South Africa posted a competitive tally of 159 for six. That probably would have been enough had they taken the opportunities presented to them.
The visitors started well. Sune Luus blasted a couple of early boundaries.
But the Kerr sisters struck back.
Jess Kerr trapped makeshift opener Chloe Tryon lbw for 14, and Melie Kerr ripped a leg-spinner past the outside edge of Luus’ bat.
Izzy Gaze whipped the bails off to stump the classy right-hander for 30.
Star South African batter Laura Wolvaardt (10 from 17 balls) tried to hit her way out of the doldrums but perished.
Jess Kerr claimed the key scalp and finished with a career-best of three for 16.
But Lea Tahuhu, who brought up her 100th T20 game in the fixture, struggled with her line.
And Devine got picked off for back-to-back boundaries in the 12th over by Annerie Dercksen.
Dercksen and de Klerk (20 from 14) teamed up to flog 17 runs off the 17th over and pile pressure back on the home team.
Dercksen swiped a reverse sweep to the boundary to close in on her maiden half century, and raised the milestone with a sliced shot into the off side.
She finished unbeaten on 55 from 32 balls but got collared with the ball.
White Ferns opener Georgia Plimmer bludgeoned four consecutive boundaries off the right-armer to add some mustard to the chase.
Melie Kerr added to the flurry of boundaries, striking three more in the next over.
The White Ferns emerged from the powerplay with a solid platform of 47 for one.
The chase was going swimmingly until Plimmer danced past the ball and was stumped for 28.
But South Africa got the dropsies after that and victory slipped away.
- South Africa levelled their T20 series 2-2 with the Black Caps last night.
South Africa made 164, Conor Esterhuizen top-scoring with 57 off 36 balls.
In reply, Tim Robinson made 32 off 22 deliveries and Dane Cleaver 26 off 16 balls, but the Black Caps were unable to forge partnerships of any real substance and paid the price, all out for 145 in 18.5 overs.
