Otago spinner Leigh Kasperek took three wickets and Suzie Bates hit 29 as the White Ferns completed pool play with their fourth win from as many games at the World Twenty20 in India.
Playing South Africa in their final pool game, the White Ferns were in complete control.
They dismissed South Africa for 99 in the 20th over and then got home by seven wickets in the 15th over in Bengaluru.
The White Ferns will play their semifinal late on Thursday and games overnight will decide who New Zealand will face in the semifinal but it is likely to be the West Indies.
In Bengaluru on Saturday night, the New Zealand team was on top early after having won the toss and sent the opposition in.
Opening offspinner Morna Nielsen made the first breakthrough in the fifth over after building up a wall of dot balls and legspinner Erin Bermingham took out the stellar pair of South African captain and first drop Mignon du Preez and No4 Marizanne Kapp.
Kasperek kept the pressure on, and had snared three wickets for 19 runs off just 3 overs to reclaim top spot as the tournament's leading wicket-taker.
She has struck nine times from four winning efforts.
The pace of Sophie Devine wreaked havoc as she mopped up the tail to have South Africa all out for 99.
Devine helped herself to three wickets in one over, although she blew the chance of a hat-trick with a wide.
Openers Bates (29 off 25 balls) and Rachel Priest (a run-a-ball 28) started very well and racked up a 57-run opening stand whipped up inside nine overs.
The White Ferns lost three quick wickets but Devine - after she survived two run-out scares - found early boundaries, and got New Zealand home safely.
Devine finished with an unbeaten 27 off 17, having thumped a trademark six over long-on at the close as she and Katey Martin brought home a comfortable win.
