The win puts the Lumberjacks (16-11, 9-4) at the No. 3 seed in the conference with three games remaining, and knocked Lamar (17-11, 8-5) down to No. 4.
SFA did not make a 3-point bucket for the second time this season, going 0 for 4 beyond the arc, but outscored Lamar 34-24 in the paint and held the Cardinals to 29 percent shooting from the floor.
Jereal Scott added 14 points and Taylor Smith had 10 for the Lumberjacks, who shot 55 percent.
Lamar got 15 points from Mike James and 10 from Stan Brown, while Devon Lamb had 15 rebounds.
SFA used a 13-1 run early in the game to go on top 19-8 and maintained a double-digit lead for most of the rest of the game.