A disciplined bowling display, led by spin duo Keshav Maharaj and debutant Prenelan Subrayen, ensured a below-par total of 164 for 5 proved enough as the hosts were dismissed for 145 in 18.5 overs.
Chasing 165, New Zealand never truly recovered after slipping from 76 for 3 to 112 for 7 in a decisive middle-overs collapse that ultimately sealed their fate. Tim Robinson top-scored with 32, but the Black Caps were unable to build meaningful partnerships, with the Proteas' attack applying relentless pressure throughout.
Gerald Coetzee set the tone early with an incisive spell of 3 for 31, before the spin combination of Maharaj (2 for 22) and Subrayen (2 for 13) dismantled the middle order. Subrayen, on debut, struck twice with well-disguised quicker deliveries to remove Dane Cleaver and Bevon Jacobs, while Maharaj's double blow in the 14th over effectively ended New Zealand's resistance.
Earlier, the Proteas' innings was anchored by a breakout performance from Connor Esterhuizen, who struck a maiden T20 international half-century, scoring a fluent 57 off 36 balls. Promoted up the order once again, Esterhuizen capitalised on his opportunity, sharing a vital 81-run second-wicket stand with Tony de Zorzi that provided the backbone of the innings.
Esterhuizen's knock was a display of controlled aggression, featuring seven fours and three sixes as he took on the New Zealand attack with growing authority. He was eventually dismissed via a stunning diving catch by Katene Clarke, who had earlier also made an impact with a lively cameo of his own.
South Africa's batting effort, however, remained a mixed one. While five of the top six reached double figures, they struggled to accelerate beyond Esterhuizen's dismissal. Jason Smith and Rubin Hermann were unable to provide late momentum, with New Zealand seamer Ben Sears particularly impressive at the death, conceding just two runs across his final two overs.
Kyle Jamieson also made an early impact with a wicket-maiden to remove Wiaan Mulder for a second successive duck, continuing South Africa's experimentation at the top of the order.
Despite fielding a depleted side, with Mitchell Santner, Devon Conway and Lockie Ferguson all rested and Tom Latham absent through injury, New Zealand briefly threatened through Tim Robinson and sporadic contributions in the middle order. However, their lack of partnerships ultimately proved decisive.
New Zealand comfortably secured an eight-wicket win over a weakened South African side at Eden Park in Auckland on Friday, taking a 2-1 lead in the five-match Twenty20 International series.
South Africa's batting coach Ashwell Prince said his team "didn't get any rhythm" after the Proteas were bowled out for 107 in a seven-wicket defeat to New Zealand in Hamilton, leveling the T20 series 1-1.
The Proteas crumbled with the bat to go down by 68 runs against New Zealand in the second T20I in Hamilton on Tuesday with the five-match series now level at 1-1.
South Africa Women produced a composed and confident performance to defeat New Zealand Women by 18 runs in the second T20I at Hamilton, levelling the series after their opening loss.
