Art Steward added 14 points and Kareem Jamar 13 for the Grizzlies (17-6, 10-1), who used a 15-0 run early in the second half to nail down their sixth consecutive victory and vault into a tie atop the league with Weber State. Derek Selvig had eight assists.
Kenny McGowen and Melvin Morgan scored nine points each for the Bengals (8-15, 6-5), who shot only 24.6 percent (14 of 57) as their four-game winning streak ended.
Montana led 32-23 at halftime, but Idaho State closed within four before the Grizzlies reeled off 15 in a row for a 47-28 edge with 14:26 left.
Montana, which has won 12 of its last 13, shot 51.9 percent (28 of 54) and outrebounded Idaho State 40-27.