The White Ferns won the toss and decided to bat, with the innings starting with a Isabelle Gaze run-out dismissal by Nadine de Klerk without facing a delivery.
Opener Georgia Plimmet [63 off 44] and skipper Amelia Kerr [78 off 44] then put on an excellent 146-run partnership for the second wicket before the captain was caught off the bowling of Masabata Klaas in the 14th over.
Wicketkeeper Sinalo Jafta was in the action again after stumping out Georgia Plimmer off Nonkululeko Mlaba's bowling to leave the hosts 155/3 and with new batters at the crease.
None of the lower order could get more than 15 runs each, with New Zealand losing regular wickets to end the innings at 190/7.
In response, the Proteas women's team found themselves struggling at 17/2 during the powerplay after losing Sune Luus [10] and captain Laura Wolvaardt for a duck.
Things got worse for the visitors when Annerie Dercksen [7] was run out by Rosemary Mair before Sophie Devine [4-12] got the wicket of Chloe Tyron [9] to leave them reeling at 55/4 after 12 overs.
South African opener Tamsin Brits [29 off 35 balls] attempted to accelerate the run rate alongside Nadine de Klerk but was caught by Amelia Kerr off Devine's bowling before the latter was bowled by the same bowler.
Kayla Reyneke powered 24 runs off 18 not out deliveries but could only help her side reach 110/7 in their allocated 20 overs.