Beamon's steal and layup gave Manhattan a 66-63 lead with 1:22 left. The Jaspers scored 21 points off of 17 Canisius turnovers.
RaShawn Stores added 15 points, including three 3-pointers, for Manhattan (22-7, 15-5). Michael Alvarado, averaging 12.4 points, did not play because of an ankle injury.
Beamon scored six of Manhattan's final 10 points of the first half as the Jaspers held a 45-32 lead. His 3-pointer was Manhattan's only field goal in the first 12-plus minutes of the second half.
Chris Perez scored 13 points for Canisius (20-11, 14-6) and Billy Baron added 10, on 2-of-10 shooting.
Canisius tied the game at 63 on a Perez 3-pointer with 3:17 left, but those were the last points the Golden Griffins would score.