Bembry finished with 14 points, 11 rebounds, four assists and three steals for Saint Joseph's (10-12, 4-6 A-10). Aaron Brown scored 11.
Patrick Holloway hit a 3 with 13 seconds left to pull George Mason (7-15, 2-8) within three, but Chris Wilson hit a streaking Bembry for a dunk on the inbounds pass and, after converting that into a three-point play, the Hawks led 57-51 just one second later.
Holloway hit another 3-pointer with six seconds remaining before Wilson made 1 of 2 free throws to seal it for Saint Joseph's.
A layup by Brown gave Saint Joseph's a 49-39 lead with six minutes to play, but the Hawks didn't make another field goal until Bembry's dunk.
Holloway led George Mason with 16 points. Shevon Thompson added 15 points and 16 rebounds.