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.