Guptill slammed a fiery 78 not out off just 55 balls to lead New Zealand to their target of 148, after a superb bowling and fielding effort by the hosts had restricted South Africa to a mediocre 147 for six.
Guptill was a shining light in the field with a superb run-out and a splendid catch, and was a deserved man of the match.
The in-form Guptill devastated the South African bowlers with his clean-hitting power, and his crossbat shots were particularly vicious as he collected five fours and four sixes.
Fellow opener Rob Nicol scored 13 as they put on 49 for the first wicket in seven overs before Brendon McCullum (16) joined Guptill in a second-wicket stand of 41 in 5.1 overs that all but sealed the contest.
South African captain AB de Villiers was celebrating his 28th birthday, but he wore the same bemused expression as Springbok captain John Smit has on many occasions at the Westpac Stadium, where South Africa’s rugby team were controversially knocked out of last year’s World Cup.
Morne Morkel was the one South African bowler to impress, taking one for 26 in his four overs, which included a maiden.
Lonwabo Tsotsobe was the biggest victim of Guptill’s onslaught, conceding 28 runs off his three overs, and the left-armer was hammered for one of the biggest sixes ever seen in New Zealand as the Aucklander launched a massive blow into the trusses of The Cake Tin’s roof.
South Africa were also unable to take wickets as Guptill and Kane Williamson, who was eventually run out by Albie Morkel for 24, did nothing silly in steering New Zealand to victory.
Contrasting innings by Justin Ontong and JP Duminy earlier took South Africa to 147 for six , giving them a total they could bowl to.
Clever bowling, backed by magnificent fielding, had given New Zealand another stranglehold over the South African batsmen after they had been sent in to bat and it needed an extraordinary over of hitting by Ontong to give the tourists a respectable total.
South Africa had been reduced to 52 for four after nine overs and Duminy and Ontong had struggled to find anything else but singles as they added 23 runs in the next five overs.
Ontong, who had seemingly edged a sweep off part-time spinner Rob Nicol to wicketkeeper Brendon McCullum in the previous over, then laid into offspinner Kane Williamson, ending his second over with four successive sixes, three of them to deep midwicket and the fourth over long on.
The bristling Tim Southee returned to claim Ontong’s wicket for 32 off 17 balls, taking a magnificent low return catch, and Doug Bracewell, who recently skittled Australia in a shock test win for New Zealand, then bowled a superb penultimate over that cost just three runs, two of them being leg-byes.
Fifteen runs would come from the final over, however, as Johan Botha hit Kyle Mills for a four and a six.
Openers Hashim Amla (19) and Richard Levi (13) had started brightly for South Africa, adding 24 off 20 balls, but the brilliance of Martin Guptill in the field had much to do with the visitors’ top-order woes.
Guptill dashed in from mid off and slid into the stumps to run out Amla and then snapped up a wonderful low catch at short extra-cover to remove AB de Villiers for eight after the South African captain had slapped a delivery from left-arm spinner Roneel Hira with tremendous power and timing.
A top-class delivery from offspinner Nathan McCullum had removed Colin Ingram for a two-ball duck, brother Brendon completing a juggled stumping after a foray down the pitch by the left-hander.
Duminy gave himself time to settle and refused to let the pressure get to him as he accumulated an important 41 off 37 balls, although he was fortunate to survive an lbw appeal off Williamson on 21.
Southee (4-0-28-3) and Nathan McCullum (4-0-16-1 with the new ball) did much to unsettle the South African batsmen.