Bryant (15-14, 12-6) will play a home game against Sacred Heart while St. Francis (21-10, 15-3) hosts LIU Brooklyn in the quarterfinal round of the NEC tournament on Wednesday.
Kostur scored 15 of Bryant's 31 halftime points and finished 8 of 16 from the floor. Dyami Starks added 15 points on just 2-of-15 shooting, but was a perfect 10 of 10 from the line.
Bryant never trailed in the contest and led 31-18 at the half. St. Francis closed within five points with 12:19 to play, but Kostur answered with a layup and a dunk to keep the Bulldogs in front.
Kevin Douglas scored 13 points as the Terriers combined to shoot 2 of 17 from distance and committed 20 turnovers.