When Cooper won race two from Ferris, with Waters again finishing third, the Kiwi hero had snatched back the initiative and restored his advantage to five points.
That made the mathematics painfully simple: Even if Ferris won the third and final race of the day, second place would be enough for Cooper to keep his crown for a fourth consecutive season. And that's exactly how it panned out.
Ferris won comfortably while Cooper cruised home in second, all the time watching over hisshoulder for a late charge and "spoiling" attack from Waters.
"The second race win today is what won the title for me and I got the job done," Cooper said.
The other two championship classes were a little more cut and dried.
In the MX2 (250cc) class, Takaka's Hamish Harwood (KTM) started the day with a 13-point lead over his nearest rival, Australian Jed Beaton (Yamaha), and, in the 125cc class, Ngatea's Ben Broad (KTM) was 23 points ahead of his closest threat, Taupo's Wyatt Chase (Yamaha).
Both Harwood and Broad prevailed on Sunday.
2016 New Zealand Motocross Championships final standings:
MX1: 1. Cody Cooper (Mount Maunganui, Honda) 267pts; 2. Dean Ferris (Australia, Yamaha) 265; 3. Todd Waters (Australia, Suzuki) 255.
MX2: 1. Hamish Harwood (Takaka, KTM) 259pts; 2. Jed Beaton (Australia, Yamaha) 242; 3. Kayne Lamont (Mangakino, Yamaha) 221.
125cc: 1. Ben Broad (Ngatea, KTM) 283pts; 2. Wyatt Chase (Taupo, Yamaha) 263; 3. Blake Gillard (Beachlands, KTM) 190.