Dion Wright scored a career-high 26 points on 12-of-19 shooting with three steals for St. Bonaventure (4-2). Posley was 6 of 18 from the field and had 13 points.
Wright scored to give the Bonnies a 58-50 lead with 6:15 to play. St. Bonaventure then went cold, shooting 0 of 5 from the field with a missed free throw, and had four turnovers before Posley hit the game winner.
The Bulls' Ikenna Smart made a dunk, Lamonte Bearden scored three points, and Wigginton made a pair of free throws to tie it at 58 with 33 seconds remaining.