Motley was 6 of 11 from the field for the Bearkats (9-6, 2-1 Southland), who shot 37.5 percent as a team. Gatson was 1 of 6 from the field but made all eight of his free throws. Michael Holyfield didn't score but grabbed nine rebounds.
Amos Wilson led the Cardinals (2-14, 0-4) with 12 points and eight rebounds. Lamar committed 20 turnovers, was outrebounded 43-32 and missed all three of its 3-point attempts.
SHSU, which never trailed, saw Lamar pull within 54-49 on Wilson's layup with 6:41 left. But the Bearkats scored the next nine points to ice the game.
The Bearkats have won their last four games at Lamar, but the Cardinals still hold a 19-10 lead in the series at home.