Rask held off the Flyers with 11 saves in the final period en route to his 13th career whitewash, which was preserved when forward Tyler Seguin made a sliding save in the third period while Rask was out of the net.
Seguin scored the first of three first-period goals for the Bruins, who improved to 3-1-1 in March.
Ilya Bryzgalov supplied 25 saves for the struggling Flyers, who dropped their third straight.
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