The teams will play again Saturday in Ottawa.
Reilly Smith scored twice, boosting the Bruins to their third straight win and their eighth in 10 contests.
Boston had only a 1-0 lead heading into the third period, but Krejci gave the Bruins some breathing room by scoring just 38 seconds into the stanza.
All five goals were surrendered by Robin Lehner on 42 shots. It was Ottawa's fourth loss in five games.
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