Delaware (5-3) drained 28 free throws and shot 51.9 percent from the field. Threatt made 12 of 15 free throws and Usher was 11 of 14. Carl Baptiste scored 13 points and grabbed a game-high 11 rebounds.
Karvel Anderson scored a game-high 25 points, including 3 of 5 3-pointers, for Robert Morris (3-6), and Mike McFadden added 11. The Colonials shot 44.9 percent from the field and committed 25 personal fouls to Delaware's 19.
Marvin King-Davis opened with a layup, drew a foul and sank the free throw for Delaware, which led wire to wire, including a 36-27 halftime advantage.
Robert Morris opened the second half with four quick points but Delaware quickly regrouped and pulled away, scoring 11 free throws down the stretch.
Maryland point guard Melo Trimble, considered a lock to leave the program before struggling in the second half last season, has withdrawn from the NBA draft and will return for his junior season.
Louisville's Chinanu Onuaku, who recently underwent a medical procedure to correct a heart rhythm issue detected during the combine, will keep his name in the NBA draft pool.
Andrew White III will return to the Nebraska men's basketball team next season after removing his name from the NBA draft.