Geffrard's jumper with 12:52 to play in the first half gave Stephen F. Austin (9-5, 2-0 Southland) a 19-9 lead before Southeastern Louisiana rallied to cut the deficit to 22-19 on Marlain Veal's layup.
But Geffrard's followed with a 3 and Thomas Walkup hit back-to-back jumpers to move the lead to 29-19.
Leading 43-33 at the half, the Lumberjacks used a 10-3 run to start the half and were never again challenged.
The Lumberjacks now own a nine-game conference win streak and are 37-1 against conference opponents under coach Brad Underwood. It was Stephen F. Austin's first road win of the season.
Zay Jackson led Southeastern Louisiana (2-12, 0-1) with 14 points. Veal scored 11 with six assists.