Kiwi speedster Portia Woodman bagged a record-breaking double to clinch the second leg of the series in Sao Paulo including a solo effort with two minutes remaining when scores were locked at 10-10.
It was speedster Woodman's 13th try of the tournament, surpassing her own record of 12 on the women's circuit and also becoming the first player to record 50 world series tries.
New Zealand led 10-0 at halftime through tries to Charlotte Arnopp-Scanlan and Woodman, but Australia bounced back through Charlotte Caslick and Emilee Cheery.
Woodman's decisive try was a brilliant long-range effort in a 70m sprint the line.
In the Dubai final in December, Australia lost 19-17 after conceding a try to New Zealand captain Sarah Goss after the final hooter.
The top five in Brazil finished in the same order as at Dubai, leaving New Zealand four points clear of Australia, with Canada third after they beat fourth-placed France 19-0 in the bronze play-off.
Earlier, Australia beat England 29-10 and needed a late try to get past Canada 12-7.
New Zealand scored four tries to beat the United States 28-17 in the quarter-finals before scraping past France 12-5 in a tense semi-final.
This year's six-leg world series doubles as a qualifier for the 2016 Rio Olympics, with the top four nations getting automatic berths.
LEADING STANDINGS
New Zealand 40, Australia 36, Canada 32, France 28, England 24, United States 18, Russia 14, Fiji 14, Brazil 10
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