The Grizzlies (19-1, 23-6 Big Sky) earned the top seed and hosting privileges for the conference tournament earlier on Saturday, when Sacramento State lost against Montana State.
Max Jacobsen led the Lumberjacks (8-12, 11-20) with 17 points, but only three after intermission. Northern Arizona earned the No. 7 seed in the conference tournament and plays No. 2 Weber State on Thursday.
Montana led 49-48 with six minutes remaining before a 12-1 run broke open the game.
The Grizzlies, who are 36-2 against Big Sky opponents the last two seasons, earned a bye to Friday's tournament semifinals and will play the highest remaining seed after Thursday's games.