Quincy Taylor hit back-to-back 3-pointers to cut Longwood's deficit to 75-73 with 22 seconds left. Jalen Carethers answered with a dunk, then Taylor missed a 3 and Radford made 3 of 4 free throws to seal it.
Radford (18-8, 9-4) moved into a four-way tie for first place atop the Big South Conference standings.
Radford took a 44-33 lead into the intermission after shooting 58.6 percent, including 8 of 15 3-pointers.
Longwood beat Radford in double overtime on Jan. 3.