North Texas (15-13, 6-8 Conference USA) scored 47 points in the second half, overcoming a 32-24 halftime deficit to hand Texas-San Antonio (8-19, 4-10) its third consecutive loss.
North Texas erased the first-half deficit as Williams tied the game at 53 on a 3-pointer with 10:11 left. Walton's basket tied the game again at 55 with 8:36 remaining, sparking an 8-0 run to give the Mean Green a 61-55 lead.
The Roadrunners cut the lead to 66-62 with 1:13 left, but North Texas hit 5 of 6 from the line the rest of the way to secure the win.
T.J. Taylor added 10 points for North Texas.