Another brisk half-ton from Henry Davids, Justin Ontong's middle-order blitz and three key wickets from Aaron Phangiso handed South Africa a 33-run victory - and two-one series triumph.
The seesaw nature of the three-match Twenty20 International affair continued on Wednesday, when the Proteas amassed a formidable 179 for six and then restricted the Black Caps to an insufficient 146 for nine.
Davids, for a second time on the trot, was at the fore of the Proteas' tally. The hard-hitting opener clinched a career-best 68 from just 51 balls, again scoring plenty of runs with his characterstic lofted drive.
All-rounder Ontong, meanwhile, replaced the out-of-form Richard Levi - and looks a far better prospect than his fragile predecessor. The right-hander's brisk 48 spanned a mere 30 deliveries, featuring a trio of handsome sixes.
Quickfire cameos of 28 and 22 not out from the left-handed David Miller and talented Farhaan Behardien later added the finishing touches, leaving an unchanged opposition XI a daunting chase.
A lot relied on ther performances of East London centurion Martin Guptill and captain Brendon McCullum. Neither could oblige, however, instead both perishing to spinner Phangiso.
Phangiso cherished a marked improvement on his awkward debut at Buffalo Park, removing Guptill and McCullum with clever changes in pace and length. His dismissal of James Franklin later afforded him figures of three for 25, but not the Man of the Match award, which went to Davids.
The latter half of New Zealand's pursuit never got off the ground, with batsman numbers five through 10 reaching double figures, but not one making it beyond Nathan McCullum's 17.
South Africa will consider Wednesday's result a job professsionally completed, while the Kiwis will rue their inability to replicate their performance in the second T20I. The teams will soon meet for two Tests, the first of which gets underway at Newlands in Cape Town on 2 January.