Brad Marchand added a goal and two assists for the Atlantic Division-leading Bruins, who went into the Winter Olympics break with a third win in four games.
Jarome Iginla and Carl Soderberg each notched a goal and an assist.
Chad Johnson earned the win with 26 saves.
Bobby Ryan and Patrick Wiercioch each scored for the Senators, whose two-game winning streak was snapped.
Craig Anderson yielded five goals on 33 shots before being pulled in the third period.
Robin Lehner relieved and stopped 7-of-9 nine shots the rest of the way.