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But, despite her best efforts, the Sparks' run chase unravelled when she was dismissed for 104 from 110 deliveries.
Wellington opening batsman Renee Moffitt enjoyed the best day of her fledgling career, thrashing a maiden century.
The 22-year-old left-hander scored 102 from 132 deliveries to help her side post an impressive 256. Her previous best was just 42, so it was a mighty effort.
Otago kept pace with the required run rate and was seemingly on course for a good win but the Sparks lost Bates and Katey Martin within an over and, with it, a lot of experience. The runs dried up and Otago's middle and lower order crumbled under the pressure. Wellington's Michelle Bunkall bowled seven wides but was able to keep Otago tied down at the death and finished with three for 37 from 10 overs.
Kylie Crowley was the last Otago batsman dismissed with the score on 239.
While Bates was not able to celebrate her hundred with a win, she played a cracking game. The White Ferns captain has been in sublime nick in the one-day tournament. She has scored 502 runs in seven games at an average of more than 100. Her innings featured 11 boundaries and her 100 came off 101 deliveries. She also had a pretty useful day with the ball, taking three for 36 from 10 overs.
Bates batted beautifully with Sarah Tsukigawa, who added 42 from 59 deliveries in a 76-run partnership for the third wicket. And White Ferns wicketkeeper-batsman Martin (38 from 59) added 115 runs with Bates for the fourth wicket.
Bates was caught and bowled with the score on 214 in the 41st over. When Martin was undone five deliveries later, the Sparks got the shakes.
''That made it pretty hard then,'' Sparks coach Warren Lees said.
''We were in a position where we were going all right chasing a big score.''
All-rounder Victoria Abbott was bowled for one and rookie Polly Inglis could not find the gaps in the field. She used up 16 deliveries for her five runs and Caitlin Blakely scored one from 12 before she was run out. With that, the match had slipped away.
''As soon as you lose wickets, the fields change and the bowlers become confident again,'' Lees said.
''It was a completely different game from when Katey and Suzie were batting. They could get a run a ball easily.
''What we have to do now is pick ourselves up and come back and try again.''
The sides meet again today and Otago badly needs to win to stay in contention for the final.