Ferris was forced to withdraw from the final MX1 class race of the day at Taupo because of a mysterious electrical problem, and this gave a massive points advantage to Cooper.
But by then Cooper had already won the first two races of the day to give himself a seven-point buffer even before the gate had dropped in that final race.
A third placing or better in the final race would have been enough to hand the title to Cooper anyway, and his victory in that race that Ferris failed to finish was merely icing on the cake for the Kiwi hero.
"I guess I offered Dean [Ferris] a chance to win the title when I gave up my 13-point advantage at [round three in] Palmerston North. But I won all three races today, and that was that," said Cooper.
Third overall for the series was fellow Mount Maunganui rider Rhys Carter (Kawasaki), a surprising result since he had started the day at Taupo only fifth in the championship chase.
But Carter also showed his liking for the sandy Taupo circuit, finishing third overall on the day and rocketing past Australian professionals Todd Waters (Honda) and Luke Styke (KTM) to claim the final step on the series podium.
In the MX2 (250cc) title chase, it was just a matter of defending champion Hamish Harwood staying cool to keep the crown ahead of Christchurch's Dylan Walsh (Yamaha) with Waitakere's Ethan Martens (Yamaha) third.
The 125cc class was also virtually only a two-rider battle, with Taihape's Hayden Smith finishing behind his main rival on Saturday, Karaka's Kurtis Lilly, but that was still enough to win the title.