Canisius closed the opening half with five-straight points to lead 30-23, and opened the second with a 7-0 run to lead by double digits with 17:40 remaining. The Stags (6-13, 4-5 Metro Atlantic Athletic Conference) could get no closer than eight points the rest of the way.
Robertson scored eight-straight points - including back-to-back 3's - to put the Griffins up by 16 points with 10:33 left to play. His 11 points were a career high.
Valenti shot 5 of 10 from the floor and had nine rebounds. Jamal Reynolds added 10 points for the Griffins (11-7, 6-3).
Marcus Gilbert finished with 18 points, 12 of those in the second half, and was the only Fairfield player to score in double figures.