The Proteas ended their run chase at 236-4 in 48.1 overs, easily overhauling the 231 target New Zealand set after losing the toss and being sent in to bat.
De Villiers top-scored for South Africa with 89, ably supported by JP Duminy (58), who combined with his skipper for a 139-run partnership when the Proteas were looking wobbly at 97-4.
Wicketkeeper Luke Ronchi’s gritty 99 was the standout performance for the Black Caps but he had little support apart from unlikely strike partner Trent Boult, with whom he set a New Zealand record 10th-wicket stand of 74.
The three-match series is essentially a World Cup warm-up for both sides as New Zealand prepares to co-host the tournament next year.
However, South Africa could also overtake Australia as the world’s top ranked ODI team if they complete a 3-0 whitewash over the Black Caps, who are ranked seventh.
De Villiers said he was pleased with the side’s performance, aside from his bowlers’ failure to snuff out the dogged resistance of Ronchi and Boult.
“We’ve got to finish big games of cricket, especially big games of cricket coming up, I’m thinking of World Cups and must wins,” he said. “In the World Cup, if you get teams to nine down you have to finish them off.”
New Zealand captain Brendon McCullum said he was pleased at his side’s fightback after losing early wickets and the return of veteran all rounder Dan Vettori after 15 months on the sidelines.
“There were some fighting qualities there but unfortunately the class of AB and JP towards the end meant we couldn’t win,” he said.
New Zealand, in their first ODI since January, looked rusty at the crease.
They opened cautiously after losing the toss and being sent in to bat, with Jimmy Neesham waiting until the third over to score the first boundary.
The hosts slumped to 68-5 before Ronchi and Tom Latham (29) set about rebuilding the innings, only for their 67-run partnership to end when wicketkeeper Quinton de Kock stumped Latham after he strayed from his crease pursuing a shot.
Ronchi continued to run out of partners and New Zealand slumped to 156-9, with not much expected when Boult arrived at the crease boasting a previous ODI high score of five.
The paceman dug in, even managing a six off Morne Morkel, before the innings ended with South African bowlers Vernon Philander, Morkel, Imran Tahir and Ryan McLaren all taking two wickets apiece.
South Africa received a minor scare when Boult dismissed de Kock and Faf du Plessis cheaply but the rest of the attack struggled for wickets as New Zealand attempted to defend a modest total.
Renee Roussouw (26) and Hashim Amla (38) kept the runs ticking over but failed to capitalise after making good starts.
De Villiers then lived up to his ranking as the number one ODI batsman in the world, combining with Duminy to comfortably seal the victory.
The next match on Friday is also in Mount Maunganui, with the series wrapping up in Hamilton on October 27.