"I went to sleep when I was young, dreaming about winning an outdoor championship.
"Now, it's a dream come true. I was feeling really good today."
Meanwhile, the 450cc rider in the Monster Energy Kawasaki team, Washington's Ryan Villopoto, won both 450cc races on Sunday, enabling him to extend his championship advantage to 14 points over Suzuki's Ryan Dungey with one round remaining.
Wilson will now get ready to represent Great Britain at the Motocross of Nations at St Jean d'Angely in France in a fortnight, while teammates and US 250cc series rivals Rattray and Baggett will suit up to represent South Africa and the US respectively at that event.
Villopoto and Dungey will race their 450cc bikes for Team USA in France.
With several leading riders injured, New Zealand will send a "development squad" to the Motocross of Nations this season.
The Kiwi squad heading to France is Auckland's Joel Doeksen (MX1), Rotorua's John Phillips (MX2) and Kieran Scheele (Open Class), from Elsthorpe in Central Hawkes Bay. Mangakino's Kayne Lamont will be there as the reserve rider.