Williams made four 3-pointers and nine of Harris' points came from the stripe and the Titans (4-7) shot 54.4 percent from the field.
Aaric Murray had 21 points and grabbed 12 rebounds for Texas Southern (3-7). Forty-five rebounds, 22 on the offensive end, helped Texas Southern stay close -- despite shooting 39 percent.
After not making a 3-pointer in the first half, Cal State Fullerton made three in a span of 2:17 and took a 65-56 lead. Texas Southern scored the next eight to make it a one-point game. But Williams' 3-pointers started a 9-0 CS Fullerton run for its first double-digit lead of the game at 74-64 with 4:51 left.
Cal State Fullerton made 7 of 8 free throws in the final minute to secure the victory.