Corey Edwards contributed 16 points and Marquise Moore added 15 for George Mason (7-12, 2-5 Atlantic-10), which controlled the boards 32-25 and never trailed in the second half. Thompson shot 6 of 7 from the field, including the go-ahead bucket in the first half, and went 7 for 8 at the line.
Both teams shot comparably from the floor but the Patriots held a 28-16 advantage in made free throws to snap their five-game skid.
Leading by five at the break, George Mason pulled away with a 10-0 run early in the second half capped by Edwards' 3-pointer to make it 41-29 with 15:52 left, and protected it the rest of the way.
Milik Yarbrough and Mike Crawford led Saint Louis (9-11, 1-6) with 14 points apiece.