On the back of a stunning 145 not out by Kane Williamson, a strong effort in the field which included five run-outs saw the hosts finish 27 runs short of their of target 280.
Following their one-wicket win in the first ODI, the Black Caps have taken an unassailable 2-0 lead in the best of three series, their first series win in any format in South Africa.
“I’m not going to underplay it,” captain Brendon McCullum told Fairfax NZ.
“It’s a phenomenal effort, really, to come over here as the No 9 ranked team in the world up against the (No 3) team in their own conditions and be 2-0 up is incredibly satisfying. It will probably go down as one of our biggest ever wins in the limited overs game.
“We’re very pleased, and it’s a nice way to finish off the tour after a pretty tough time.”
McCullum praised Williamson, who like many of his team-mates struggled in the test series.
“Kane Williamson’s innings was as good as I’ve ever seen from a New Zealander in one-day cricket and a few guys backed it up around him as well.
“The way we were in the field, the guys were outstanding. I’m very proud of the boys, they’ve shown a lot of character.
“Hopefully all the fans back home who have stuck by us, this is a little bit of love for them.”
Williamson’s third ODI century featured 17 fours and a six off the final ball of the innings.
He started cramping towards the end, but held on to score the equal sixth highest ODI score by a Kiwi.