The Sparks shone in the early twenty20 match, beating competition-leader Wellington by 37 runs.
The captain, Suzie Bates, led the charge with 58 at the top of the innings to help the Otago post 158 for seven.
Leigh Kasperek (30), Morna Nielsen (28) and Katey Martin (25) all made solid contributions as well.
Beth Langston removed the dangerous Sophie Devine in the opening over. But it was Kasperek who starred with the ball with four for 19.
She helped spin out Wellington for 121. Left-armer Kate Heffernan proved miserly with one for 14, while Langston was effective as well with one for 19.
Amelia Kerr top-scored for Wellington with 34.
The afternoon match did not go to plan, however. Otago struggled with the bat, limping to 137 for eight. Kasperek top-scored with 38 and Polly Inglis added a valuable 22.
Bates (16) got a start but could not go on, while Martin went early for five. The White Ferns duo have led Otago to victory so often during the last decade but not on this occasion.
Northern’s Carolyn Esterhuizen made the key breakthroughs. The South African right-arm spinner finished with four wickets for her troubles.
Medium pacer Alisha Rout produced a tidy spell, taking one for 19.
Bernadine Bezuidenhout got the chase off to a rapid start with 62, while fellow opener Natalie Dodd saw the job through with an unbeaten 55 from 49 to seal an eight-wicket win.
The loss meant the Sparks dropped to last place with two matches remaining.
