Chasing South Africa\'s 179 for 6, New Zealand succumbed to Ryan McLaren\'s pace and Aaron Phangiso\'s spin.
Port Elizabeth: South Africa recovered from the early loss of captain Faf du Plessis to reach 179 for 6 and Aaron Phangiso and Ryan McLaren shared six wickets to beat New Zealand by 33 runs in the series-deciding Twenty20 on Wednesday.
The Black Caps were 146 for 9 in reply in their 20 overs after South Africa rode a tricky start to win the decisive game at St. George's Park and take the series 2-1.
Opener Henry Davids made 68 for the home team and Justin Ontong hit a quickfire 48 from 30 balls on his recall to the T20 team to revive South Africa after they were 26 for 2 and struggling in the fifth over.
Left-arm spinner Phangiso then took 3 for 25 in just his second international and combined with McLaren, who also took 3 for 25, to keep New Zealand out and ensure South Africa started their home season with a series win. The teams meet in the first of two Tests starting on January 2.
"This is my first time captaining," new skipper Du Plessis said. "We have been consistently good in all games and it's been a good learning experience for me."
Du Plessis had been dismissed for 1 by impressive newcomer Mitchell McClenaghan (2 for 24) after being promoted to open following the dropping of Richard Levi and de Kock was out for 2, also to McClenaghan, to leave South Africa in trouble.
Davids hit seven fours and two sixes in his second half-century in two games and Ontong counter-attacked from No. 4 with three sixes and a four after being recalled for the out-of-form Levi to eventually take South Africa to a winning total. David Miller made 28 and Farhaan Behardien 22 at the end.
Doug Bracewell took 2 for 35 for New Zealand after removing both Miller and Behardien in the final over but by then South Africa had already set the visitors a tough target to take the series.
Guptill, New Zealand's century-maker and match-winner in the second game, hit three fours and a six at the top of the Black Caps' innings but he was the first of Phangiso's three wickets when he holed out to Robin Peterson.
Captain Brendon McCullum top-scored with 25 but also fell to Phangiso as New Zealand lost Guptill, McCullum and Colin Munro for seven runs and couldn't recover.
"South Africa played well in those clutch moments," McCullum said. "We were 10 percent off throughout and against a good side that exposes you. 160 to 165 would have been a really pleasing score to keep them to, but they played well in the back half of their innings.
"Had our top order got going, we could have been competitive but we could not get those partnerships."