The Sparks are in second place in the Hallyburton Johnstone Shield standings with 25 points.
But Northern Districts and Central Districts can both still overhaul Otago if they win their remaining two round-robin games.
Wellington is through to the final.
Sparks coach Craig Cumming said his side produced a flat performance.
"It was a bit disappointing. We waited a day and a-half to play some cricket [after Saturday’s game was abandoned due to rain] and I think we played like we had been sitting around," he said.
"We felt we had a good chance to win it at halftime. Olivia Gain was batting well but unfortunately she was run out.
"We had a lot of good starts but no substance and no partnerships of note."
"We were a little flat."
The game reduced to a 33-over contest. Blaze opener Jess McFadyen carried her bat with a knock of 76 to help her side post 159 for seven.
Georgia Plimmer chipped in with 38, while Saffron Wilson picked up three wickets for Otago.
Spinner Eden Carson’s two for 28 represented good value as well.
But Wellington’s spin duo of Leigh Kasperek and Xara Jetly nabbed three wickets apiece.
Gain made 20 at the top of the order and stand-in captain Kate Ebrahim top-scored with 31.
Polly Inglis (14), Wilson (17) and Paige Loggenberg (11) got started but could not go on.
The Sparks were without White Ferns trio Suzie Bates, Katey Martin and Hayley Jensen, so named two new caps in the starting XI.
Loggenberg showed promise during her innings, while spinner Chloe Deerness was not needed at the bowling crease.
"It was tough for Chloe not to get a bowl but when it is only 33 overs it is tough," Cumming said.
"But she has her first cap now and had had a taste of it.
"And Paige was looking really good with the bat. She showed a lot of potential."
Rain ruined two of the three Hallyburton Johnstone Shield games on Saturday.
But in Hamilton Northern Districts recorded a comfortable seven-wicket win against Canterbury.
Nensi Patel nabbed five for 46 to help restrict Canterbury to 229 for eight.
Openers Kate Anderson (46) and Caitlin Gurrey (58) put on 81 for the first wicket and Holly Topp scored 47 to help their side cruise past the target with more than nine overs to spare.
