Lamoureux, who has already qualified for the 2006 Winter Olympics, landed a score of 45.20 from the judges, missing the silver medal by 0.5 points and the gold by 0.8 points.
The win went to Tommy Czeschin, followed by Travis Rice.
Lamoureux was joined in the top-10 by two Canadians, Hugo Lemay in eighth and Brad Martin in 10 th .
In the womens event, it was all stars and bars, with Hannah Teter finishing first by a five point margin. Kelly Clark was second and Elena Hight third. None of the Canadian women made the final eight, and Naho Mizuki of Japan was the only non-American in the finals, finishing seventh.
The other events in Grand Prix season are at Mt. Bachelor in Oregon from Jan. 6 to 9 and at Mountain Creek from Feb. 4 to 5 2005.