Montana (5-1, 1-1 Big Sky Conference) grabbed a 7-0 lead on Bergquist's 39-yard strike to Mariani with 8:43 left in the first quarter, just one play after the Grizzlies' Severin Campbell got a hand on a punt attempt by Fritz Brayton of Eastern Washington (2-4, 1-2).
With a sweeping wind limiting each offense to just one field goal over the next two quarters, the Grizzlies went up 17-3 early in the fourth.
Andrew Schmidt broke through the line to block another Brayton punt and Erik Stoll recovered on the Eastern 8-yard line. On the ensuing play, Bergquist hit Mariani again -- his ninth TD reception of the season.
Montana went up 19-3 with 6:21 left in the game when Eastern Washington quarterback Matt Nichols was called for intentional grounding from his own end zone. Nichols, who entered the game averaging nearly 344 yards passing with 12 touchdown passes, was limited to 19-of-45 for 191 yards.
Bergquist finished 15-of-25 for 199 yards for Montana, which had no turnovers after giving up the ball nine times in its previous two games.
Mariani caught five passes for 118 yards for the Grizzlies, who have won three straight against the Eagles and five of the last six meetings between the teams.
Eastern Washington had a chance to strike first, marching the opening kickoff to the Montana 25. Running back Alexis Alexander raced 22 yards on a sweep before fumbling into the end zone, where it was recovered by the Grizzlies' Shann Schillinger.
Defensive end Greg Peach had four sacks for Eastern.