Smith missed 13 of 17 shots from field but made up for it shooting 12 of 15 from the foul line. Nigel Ribiero added 10 points for Grambling (11-12, 7-3 Southwestern Athletic).
With Grambling leading 69-66, Smith fouled Jared Sam with five seconds left after he converted a layup to reduce Southern's deficit to a point. But Sam missed the potential and-1 chance to tie it and time ran out.
Sam's layup gave Southern a 41-32 lead with 13:32 left. Grambling later went on an 8-0 run and Jackson tied it at 45 with a dunk. The teams traded leads before Jackson made two foul shots for a 61-60 lead that Grambling never gave up. Ribeiro made two fouls shots for a 69-66 lead with 15 second left.
Sam led Southern (9-14, 5-5) with 23 points on 7-of-10 shooting from the field and 9 of 11 from the free throw line and Aaron Ray scored 14.
Mike Krzyzewski switched to zone last season to mask his young team's defensive frailties. Will we see that again in 2018-19?
The cream of the crop of American high school basketball will congregate in Colorado Springs from Oct. 5-7, as USA Basketball unveils its newly expanded Junior National Team minicamp in collaboration with the NBA, NCAA and NBPA.
Missouri guard Cullen VanLeer is retiring from basketball after tearing his ACL in the Tigers' final regular-season game last season.