Spencer kept the Tigers in the game during the first half when he scored 12 of his points, while Thornton made four 3-pointers in the second half.
LSU (10-1), which led 25-23 at halftime and trailed by seven points midway through the second half, ended the game on a 24-5 run. Thornton had eight points during that outburst, while Garrett Temple scored six of his season-high 13 points and Spencer added five points.
The Tigers held a two-point advantage heading into the final five minutes. On two occasions, Aron Baynes made field goals to pull Washington State (8-4) within a point -- the last time at 53-52.