The opener smashed 101 from 69 delivers with the hard-hitting right-hander pounding a boundary off the final ball to secure the win.
South Africa made a handy 165 for five after being put into bat and the BLACKCAPS needed every one of their 19 overs to reach the duckworth-lewis adjusted target of 169.
Guptill, who missed the last match with a stomach bug, put on 76 for the first wicket with the partnership broken when Rob Nicol was caught on the boundary for 25.
Brendon McCullum supported with 17 but his innings ended with 12 balls remaining bringing Colin Munro to the crease.
There were a number of dropped chances by the South African fielders but none more important than when Robin Peterson shelled Guptill with 19 required off 10 deliveries.
Guptill fittingly found himself on strike with four required and hit the winning runs to spark celebrations from the New Zealand dug-out.
Earlier, Ronnie Hira removed Richard Levi cheaply but Henry Davy and Faf du Plessis combined for a 68 runs stand and it wasn’t until the 12th over that the partnership was broken.
Davy pounded 55 off 38 deliveries with Jimmy Neesham talking a stunning catch to send the South African opener back to the dressing room.|
At 7.10pm a set of lights went out only with play stopped until 8.00 leading to the the match being reduced to 19 overs per side.
David Miller freed arms with a rapid 33 while captain Du Plessis was impressive with his sides top score of 63. Both batsmen were out in the final Doug Bracewell over with the fast bowler also picking up Farhaan Behardien off the penultimate ball.
Nathan McCullum was economical , going for 23 off his four overs while Bracewell finished with three for 33.
