After edging the Kiwis 57-54 in Auckland three days ago, Australia were ruthlessly efficient across all four quarters at Horncastle Arena.
They trailed early, but never looked back after hitting the front late in the first quarter.
Maria Tutaia again started in the shooter's circle for New Zealand, with Bailey Mes out at goal attack, and the Ferns kick-started the quarter with three quick goals.
While the Diamonds took some time to fire in the front third, their through-court defence was as uncompromising as ever, and the pressure eventually told with a steady stream of turnover ball.
With goal shoot Caitlin Bassett dominating the front space, and with goal attack Susan Pettitt equally adept on the shot or feed, the Diamonds stormed back to close the spell with a five-goal run to lead 14-11 at the first break.
The Australians continued to dominate through the middle in the second stanza, opening out to a six-goal lead midway through the spell before Ferns coach Janine Southby rang the changes.
Tutaia shifted out to goal attack, while Te Paea Selby-Rickit replaced Mes (10 from 13) at goal shoot, and the Kiwis scrapped their way back with two late goals cutting back the Diamonds lead to 29-26 at half-time.
Circle defenders Courtney Bruce and April Brandley continued to generate turnover ball throughout the third quarter, with midcourters Kim Ravaillion and Liz Watson shifting the bonus possession downcourt.
Pettitt was replaced by Steph Wood at the main break, the 25-year-old slotting into a familiar shooting circle combination with Sunshine Coast Lightning teammate Bassett.
From then on, the Diamonds controlled play, both on attack with a pacy midcourt drive and on defence, where they pushed the Kiwis wide and slowed down the circle feed.
The Ferns kept battling, Tutaia nailing a spectacular long bomb right on the buzzer, but the Diamonds still took a 44-39 lead into the final quarter.
There was no chance of a last-gasp comeback, the Australians controlling the tempo right to the final whistle to wrap up the win.
The teams now to travel for the third Test in Adelaide on Wednesday, with the final match in Sydney three days later.