The Lumberjacks (8-1), who entered the game leading the nation in scoring defense (49.5 points per game), led by as many as 11 in the second half. Oklahoma (7-3) had a chance to tie in the final seconds but failed to convert a pair of free throws.
Stephen F. Austin methodically worked the ball inside, scoring 34 of its 56 points in the paint. The Southland Conference member held Oklahoma to its second-lowest scoring output this season.
The Lumberjacks took their first lead with 9:59 remaining in the first half on Smith's left-handed jam, but Oklahoma closed the half on a 17-9 run to lead by four at the break.