Lamar (3-1) rolled in the second half, with Berry throwing a 17-yard touchdown to Devonn Brown and Harris breaking off a 37-yard scoring run.
Dillon Barrett had five receptions for 93 yards and Begelton finished with 70. Lamar piled up 661 total yards.
The Choctaws, an affiliate of the National Christian College Athletic Association, tied the game on their first drive when quarterback Kyle Smith scored from 12 yards out. Hunter Estess' field goal made the score 14-10, but Lamar rolled from there.
Chris Ingram led the Choctaws with 104 yards on 16 carries.