Tyler Gron and Chase Schaber scored late third-period goals to seal a 5-3 victory over the Colorado Eagles on Sunday in Loveland, Colo.
Gron finished with two goals, and Adrian Foster rounded out the scoring for Idaho.
Tyler Beskorowany picked up the win in net, stopping 29 shots.
The win gives Idaho a 3-1 lead in the Western Conference playoff series. Game 5 is Tuesday night in Colorado, when the Steelheads have a chance to clinch the series.