Tim Rusthoven added 13 points for William & Mary (6-3).
Ahead 32-31 early in the second half, Thornton made a layup and connected from 3 to push the Tribe's lead to six, 37-31, with 17:43 left in the period.
Radford (5-5) trailed by single digits most of the second half until Rusthoven's tip-in and two free throws extended William & Mary's lead to 10, 57-47 with 3:36 left to play.
Kion Brown led Radford with 13 points and nine rebounds.
Michigan has hired assistant basketball coaches Billy Donlon and Saddi Washington.
Duke and Cincinnati, 2016 NCAA tournament teams, highlight the eight-team field for the Naismith Memorial Basketball Hall of Fame Tip-Off Tournament.
NCAA champion Villanova will play Notre Dame and Pittsburgh will play Penn State in the inaugural Never Forget Tribute Classic at Prudential Center on Dec. 10.