Krejci snapped a 1-1 tie with his score early in the middle period, and then set up a Milan Lucic goal in the third.
Reilly Smith scored and added an empty-netter for Boston, which earned a split of a home-and-home series against the Sabres.
Tuukka Rask stopped 34 shots.
Zemgus Girgensons got Buffalo's only goal. Jhonas Enroth turned aside 35-of-38 shots for the Sabres.