The classy White Ferns all-rounder thumped 88 from 57 balls to help her side post an intimidating 159 for three.
Sparks captain Suzie Bates flogged 70 from 55 balls. But the home side was unable to keep pace with the required run rate and the chase fizzled out at 139 for seven.
Otago coach Craig Cumming conceded the last five overs of Wellington’s innings had been too costly.
The visitors clubbed 63 runs in that period.
"I don’t think our fields were quite right and I was hoping for 145-150," he said.
"I thought that would be a good effort because it is a wonderful batting surface with a fast outfield.
"We just leaked a few in that back end. But you can put that down to some quality batting as well.
"They are a good team. Melie batted really well and didn’t give any chances."
Otago strike bowler Emma Black produced another quality spell at the top of the innings. She got the wicket of Rebecca Burns and went for just 10 runs from the first three of her four overs.
That brought Kerr to the wicket and she looked assured immediately.
She played a lovely drive down the ground and pulled another through midwicket.
The classy 23-year-old all-rounder stroked back-to-back boundaries off PJ Watkins’ only over to lump some pressure on the home side.
Jess McFadyen got into the spirit as well and ramped Watkins over the keeper for four.
It was a costly 14-run over and Kerr was taking over. She cut White Ferns team-mate Eden Carson for four and slapped the next to long-on for another boundary.
The visitors had maneuvered themselves into a commanding position at the halfway stage at 67 for one.
English import Linsey Smith bowled McFadyen for 23 but Kerr continued her march towards a half century, which came up off 40 balls.
Georgia Plimmer was put down for three at cover. But the wicket the Sparks really needed was Kerr, and she was doing a wonderful job of either finding boundaries or hitting the gaps for two.
She moved into the 80s with an exquisite lofted drive to long-off. The next ball from Suzie Bates was deposited over the midwicket rope for six.
But Kerr danced down the wicket and was stumped next ball.
The Blaze smashed 14 off the last over to set a challenging chase.
Bates found the middle of her bat early for Otago. She clouted back-to-back boundaries off Leigh Kasperek and crushed a delightful drive down the ground off Jess Kerr.
Bella James timed the ball nicely before her promising knock of 21 was cut off by Burns, who leaped high and pulled in a smart catch at short thirdman.
Otago was also 67 for one at the halfway stage. The game was perfectly balanced.
Bates and Caitlin Blakely (28) put on 60 for the second wicket.
But the Sparks’ fate rested firmly on Bates’ shoulders.
She targetted Natasha Codyre and lapped consecutive boundaries.
But her fine innings came to an end when Xara Jetly (three for 28) slipped a delivery under her bat and she was stumped.
Olivia Gain perished the same way next ball.
Hayley Jensen saw off the hat-trick ball but that double breakthrough effectively ended the game as a contest.
