Will Cherry and Raason Young added 11 points each to help the Grizzlies (20-9) dominate Northern Arizona for the third time this season.
Montana advances to the Big Sky semifinals Tuesday against No. 2 seed Northern Colorado in Ogden, Utah.
Cameron Jones led Northern Arizona (14-14) with 21 points.
The Grizzlies jumped out to a 7-0 lead and never looked back, leading the game from wire to wire.
Montana dominated Northern Arizona in almost every facet of the game, but it was most noticeable on the glass where the Grizzlies outrebounded the Lumberjacks 41-29.