Lamont followed that win by finishing second and third in the following two races, enough to win the day by seven points from yet another KTM rider, Kale Makeham.
Previous championship leader Wilson finished the day only fourth overall, slipping back to 19 points behind Lamont in the title chase.
"I've gone from nine points behind to 19 points in front. It has been a great day," Lamont said.
"I want to thank the CMR race team, Shift apparel, Dragon goggles, Jeff Leisk at KTM Australia, Bike-sportNZ.com, John Appel and the Cachia family for their support."
Also racing in the under-19 class in Australia this season, Rangiora's national junior motocross champion Micah McGoldrick (CMR Red Bull KTM) finished the day 21st overall.
He is now 25th overall in the championship standings.