Montana (12-10, 8-3 Big Sky) snaps a two-game losing skid and remains in third place, two games back of conference leader Sacramento State (16-6, 10-1).
Gregory made 4 of 8 field goals and was 7 of 7 from the line. Martin Breunig scored 12 points, Brandon Gfeller had 11 and Mario Dunn chipped in 10 for the Grizzlies, who shot 50 percent from the floor.
Montana finished the first half on a 14-3 run to build a 32-24 halftime lead. Idaho pulled within 60-54 with 2:58 left before Montana closed on a 10-2 surge to seal it.