Williams, Kyan Anderson and Hank Thorns each converted two free-throw attempts within the final 1:36 for TCU (14-10, 4-4 Mountain West).
Thorns scored 15 points, J.R. Cadot 14 and Garlon Green 10 to supplement Williams’ output.
Anderson had eight assists and three steals and Cadot and Connell Crossland each had seven rebounds.
Williams’ effort helped TCU to a 30-8 scoring advantage off the bench.
Wes Eikmeier scored 26 points for Colorado State (15-8, 4-4). Pierce Hornung scored 14 points and grabbed nine rebounds.