Brad Marchand added two goals and a helper and Patrice Bergeron contributed three assists for the Bruins, who are seeking to avenge an historic collapse against the Flyers in last year's Eastern Conference semifinals.
Tim Thomas stopped 31-of-34 shots for the third-seeded Bruins, who led 3-games-to-none in last year's series but then dropped four straight to Philadelphia -- only the third time in NHL history that had happened.
Danny Briere, James van Riemsdyk and Mick Richards scored for the second-seeded Flyers.
Philadelphia goalie Brian Boucher was pulled late in the second period after yielding five goals on 23 shots. Sergei Bobrovsky came in and stopped 8-of-10 shots the rest of the way.