Gron's first goal gave Idaho a 1-0 lead in the first period. After a tally from Adrian Foster made it 2-0, Colorado tied the game with two second-period goals.
Austin Smith took a beautiful pass from Austin Fyten to give Idaho the lead back late in the second period - and Idaho killed off three third-period Colorado power plays to seal the victory.
The Steelheads lead the series 3-1, with game five in Colorado Tuesday. If necessary, Game six would be back in Boise.