Clark made 8 of 16 from the field, including 3 of 4 from 3-point range, and made all of his 11 free-throw attempts. Marquis Salmon had 17 points and 14 rebounds, both career highs, for Texas Southern (6-16, 6-3 Southwestern Athletic Conference).
Clark scored five points during a 9-2 run that made it 30-22 with six minutes left in the first half and the Tigers led the rest of the way. Alabama State trimmed its deficit to seven points on three occasions in the second half but got no closer.
Texas Southern outscored the Hornets, who committed 30 fouls, 36-12 from the free-throw line.
Mannion, who recently reclassified and is ESPN's No.11 overall player in the class of 2019, chose Arizona over Marquette.
He'll fit in with Sean Miller's plans for a faster tempo on offense.
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.