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.
Kendrick Nunn, who pleaded guilty to misdemeanor domestic battery last week, has been dismissed from the Illinois basketball team.
Delaware has hired Notre Dame assistant Martin Ingelsby as its next men's basketball head coach, sources told ESPN's Jeff Borzello.
Michigan State-Duke in the ACC/Big Ten Challenge will pit two of the best recruiting classes in the nation. Here's a look at all the games.