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Heading into the final match of the three game series, the teams were locked at one-all after splitting the opening fixtures in a double-header on Tuesday.
A superb bowling performance today had the Australians on the back foot soon after the Ferns won the toss and elected to take the ball in blistering conditions at Melbourne's Junction Oval.
New Zealand were led by 22-year-old Morna Nielsen, who took 1-9 off her four overs at the front of the innings and picked up the cheap wicket of Alyssa Healy in her second over.
But it was Nielsen's searing economy rate that heaped the pressure on the hosts, who eventually struggled to a light total of 134/5.
Chasing a run rate of six and over for victory, Lucy Doolan (35 off 40) and skipper Suzie Bates (67 off 44) then poured on a 101-run opening stand to cruise to an emphatic seven-wicket victory with two overs to spare.
Both sides now travel to India for the world cup, which begins January 31.