Chris Hass finished with 14 points and Stephen Brown added 12 for the Bison (11-9, 8-1 Patriot League), who have started 8-1 or better in conference for the ninth time in the schools' 25-year history in the conference.
Bucknell hit 27 of 34 at the line and grabbed 16 offensive rebounds.
A layup by Lafayette's Paulius Zalys cut the Leopards' deficit to 57-53 with 5:42 remaining. But the Bison scored 11 of the game's next 16 points, capped by two Brown free throws and a MacLeay layup, and took a 68-58 lead with 2:57 left.
Bryce Scott's 3 cut it back to seven, but the Leopards could not get closer.
Scott led Lafayette (5-14, 2-6) with 17 points.