Sherrod Wright scored 15 for George Mason while Jonathan Arledge and Mike Morrison added 12 apiece for the Patriots, who shot 57.8 percent (26 of 45) from the field.
George Mason (13-5, 5-1 Colonial Athletic Association) opened the game on an 18-9 run and pushed that advantage to 21, 43-22, en route to a 45-30 halftime lead.
The Patriots led by as many as 24 in the second half before James Madison fought back to within 10, 82-73, with less than two minutes to play.
George Mason held the Dukes to 9 of 31 shooting in the first half and 6 of 21 from 3-point range.
Humpty Hitchens and Devon Moore led James Madison with 19 apiece and A.J. Davis added 17 but the Dukes’ (8-9, 1-5) bench only contributed 11 points.