Chasing 169 for victory in 19 overs at Buffalo Park, Guptill helped erase the memory of Friday's embarrassing capitulation to 86 all out in Durban with a stunning batting display as the tourists reached their target for the loss of just two wickets to level the series 1-1.
Requiring 39 from the final four overs and 11 off the last, Guptill was on 97 and needing four for victory when Rory Kleinveldt bowled the final delivery - a low full toss which was eased away through extra cover.
Guptill's unbeaten 101 was just the third T20 international century by a New Zealander, the first two belonging to captain Brendon McCullum who was almost anonymous with 17 from 15 balls during a second-wicket partnership of 73 with Guptill.
The right-handed opener was similarly dominant during an opening stand of 76 with Rob Nicol (25) as he drove the Proteas attack impeccably straight and displayed the skills - and patience - so obviously missing from the New Zealand batsman in Durban.
Captain Faf du Plessis led from the front once again as South Africa posted a competitive 165-5 in 19 overs after losing the toss and being asked to bat first.
Du Plessis paced his innings to perfection on a tricky pitch to reach 63 from 43 balls with eight fours and a six in a match reduced to 19 overs per side following a 52-minute floodlight failure.
The deciding match takes place in Port Elizabeth on Wednesday. (Editing By Alison Wildey)
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