Stockton took a 2-1 lead with six minutes, 42 seconds remaining in the third period on a goal by Maxime Boisclair. The Thunder extended it to 3-1 with a goal late in the third period by Ryan Hayes.
Idaho had tied the game at 1 on a goal by David de Kastrozza early in the second period. An apparent Stockton goal just moments later was waved off by the referee.
Stockton took a 1-0 lead on a goal by Andrew Clark in the first period.
Idaho out-shot Stockton for most of the game.
Game 2 is Sunday at 5 p.m. at CenturyLink Arena in Boise.
Click below for updates throughout the game.