Ogunyemi led Siena (3-2) with a career-high 24 points on 12-of-19 shooting. Brett Bisping had 16 points and 16 rebounds while Marquis Wright added 15 points and nine assists.
Zach Thomas had 20 points to pace Bucknell (3-2). Chris Hass had 18 points, Nana Foulland scored 13 and Stephen Brown added 12 points.
Bisping's layup with 47 seconds left in OT put Siena up by three. But Thomas made a pair at the line and Hass' driving layup tied it at 81 with 13 seconds left. Wright broke down the Bucknell defense and found an open Ogunyemi for the game-winner inside. Hass had a chance to tie but missed at the buzzer.
Bisping made 1 of 2 free throws with 1 second left in regulation to force overtime.