George Mason held a five-point lead with 41 seconds to go but was unable to hold on for the upset.
The Patriots turned the ball over on their final two possessions, the first miscue leading to a layup attempt by Chez Williams.
Williams missed that effort, but Gordon was there for the offensive rebound and put it in to give the Minutemen the lead. George Mason then turned the ball over again and wasted its final chance at a victory.
Massachusetts climbed to 15-1 for the season and to 3-0 in Atlantic 10 Conference play. Williams scored 26 points and had eight assists. Cady Lalanne added 19 points and nine rebounds before fouling out.
The Minutemen shot 54 percent from the field and hit 6-of-14 from 3-point range.
George Mason (7-10, 0-3 A-10) was led by Sherrod Wright with 26 points.