Martin Breunig and Brandon Gfeller had 10 points apiece for Montana (18-11, 14-4), which will share the regular season title with Eastern Washington but host the tournament as the No. 1 seed because of a tie-breaker.
Montana, which shot 51 percent from the field, trailed 21-13 midway through the first half but overtook Montana State with an 11-0 run capped by Dunn's jumper and carried a 31-27 advantage into the break. The Grizzlies continued to pull away in the second, taking its largest lead of the game with a layup from Dunn that made it 66-46 with 4:37 left.
Marcus Colbert led Montana State (7-23, 4-14) with 17 points, Stephan Holm added 13 points and Michael Dison had 10.