Chasing a target of 177, the tourists were bowled out for a paltry total of 107 in 15.3 overs with Kiwi seamer Lockie Ferguson recording figures of 3-16.
The Proteas lost wickets at regular intervals chasing a middling target on what seemed a good pitch at Seddon Park with paceman Ben Sears also taking three wickets.
Only George Linde, batting at number seven, showed any fight with the willow as the Western Province allrounder struck 33 from 12 balls before being the last man dismissed.
Earlier, the Black Caps relied on a strong finish to the innings to get to a total of 175-6 in their 20 overs after being sent in to bat at the toss.
Opener Devon Conway top-scored with a measured 60 off 49 deliveries while Nick Kelly contributed 21 and captain Mitchell Santner hit 20.
The late impetus though was provided by Cole McConchie (18 not out from 12) and Josh Clarkson (26 not out off 9) as the pair shared in an unbroken partnership of 35 from just 13 balls.
The third T20I of the five-match series will take place in Auckland on Friday.
Proteas coach Shukri Conrad says the "jury is out" on whether the T20I series in New Zealand should have been given international status but insists the tour has been an "invaluable exercise".
The Proteas levelled the five-match T20I series against New Zealand in Wellington on Sunday, securing a tense 19-run victory in the fourth match to set up a decisive final clash in Christchurch on Wednesday.
New Zealand comfortably secured an eight-wicket win over a weakened South African side at Eden Park in Auckland on Friday, taking a 2-1 lead in the five-match Twenty20 International series.
South Africa's batting coach Ashwell Prince said his team "didn't get any rhythm" after the Proteas were bowled out for 107 in a seven-wicket defeat to New Zealand in Hamilton, leveling the T20 series 1-1.
