Dungey, the Red Bull KTM rider from Belle Plaine, Minn., beat Mike Alessi in both motos.
"Mike put up a fight in both motos," Dungey said. "It was a crazy one. These were the toughest conditions I've experienced here, but the bike worked really well throughout the day. Every race and every championship series goes differently, so I'll keep my head down and go one race at a time.
"To celebrate the win is awesome. You've got to enjoy it, but it's time to go to work again. You're only as good as your last race and you've got to be there every single weekend."
Dungey extended his lead in the 450 Class standings to 42 points over Alessi, the MotoConcepts Suzuki rider from Victorville, Calif.
James Stewart, the Team Yoshimura Suzuki star from Haines City, Fla., finished fifth in the first moto aboard, then skipped the second mote because of the effects of a crash at the previous stop.
"Halfway through the first moto I could barely hold on," said Stewart, who swept the first two events of the season. "I was struggling a bit because I got a bad start, but I was working my way up. I was trying to do my best to hold on and I almost fell over a few times."
In the 250 Class, GEICO Honda's Eli Tomac, from Cortez, Colo., also won for the second time this year, finish second in
In the Women's Motocross Championship, Rockstar Energy Racing Suzuki's Jessica Patterson, from Tallahassee, Fla., took the overall win. She was second in the first moto and won the second.