Their powerful top order powered them to 154 for seven after they won the toss and batted and their varied bowling attack then smothered Sri Lanka to restrict them to 107 for eight in reply.
The win was the Kiwis women’s second following their easy win over India on Thursday and it put them at the top of Group B on four points.
Player-of-the-Match Suzie Bates stroked an attractive even fifty at the top of the order, posting 54 for the first wicket with captain Aimee Watkins who hit 20 from 21 balls.
The right-handed Bates hit six fours in an innings that required just 43 balls before becoming the first of medium pacer Chamani Seneviratne three wickets at 88 for two in the 14th over.
Before she fell, Bates added another 34 for the second wicket with Sarah McGlashsan who was in superb form, thrashing the Sri Lankan bowling for 31 off 23 balls with two fours and two sixes.
New Zealand lost both McGlashsan and Sophie Devine (5) in successive overs to slip to 112 for four in the 17th over before Nicola Browne (20) and Liz Perry (19) posted a cameo 36 from 20 balls for the fifth wicket, to bring the innings to a rousing end.
Sri Lanka made a promising start when Chamari Atapattu (21) and Dedunu DaSilva (14) added 32 from 27 balls for the first wicket but when Atapattu fell in the fifth over, the innings fell apart.
Wickets tumbled repeatedly and though Suwini de Alwis struck a defiant 26 from 24 balls, Sri Lanka could not find the momentum to get over the line.