Gardner was the hero in the 62-59 win over Lehigh on Wednesday when he nailed a 3-pointer as time expired.
Lafayette trailed throughout the second half until Nick Lindner stole the ball from Gardner and drove for the layup to tie the game at 76 with 7.1 seconds remaining.
Gardner, who finished with 19 points on 6-of-8 shooting, calmly made the shot to give American (11-7, 4-2 Patriot) the win. He also hit both of his 3-pointers, made all five free throw attempts and had nine assists.
Dan Trist had 25 points, Lindner added 17 and Seth Ninrichs had 11 for Lafayette (11-6, 3-3).