Clark was 24-for-37 for the Mountain Hawks (2-5, 2-0 Patriot League) and threw a 5-yard scoring pass to Alex Wojdowski with 5 seconds left in the first half for a 21-7 lead.
Jake Drwal caught nine passes for 124 yards as Lehigh's offense totaled a season-best 461 yards.
Lehigh's other four touchdowns were running plays: Michael Colvin from 4 yards out, Clark and Zach Barket on 1-yard bursts and Jaren Walker on a 2-yard rush.
Marcello Trigg was 14-for-26 for 216 yards with one touchdown for Bucknell (3-4, 1-1). Trigg connected with Shaun Pasternak on a 43-yard scoring play for the final margin.
The Mountain Hawks have beaten the Bison 12 straight times, including six consecutive in Lewisburg.