Rask was busiest in the second period when made 15 saves as Boston was getting tallies from Gregory Campbell and Johnny Boychuk to grab the lead.
Brad Marchand and Tony Krug each contributed a goal and a helper while Milan Lucic also scored for Boston, which won a second straight home game beginning its Eastern Conference semifinal series.
Patrice Bergeron and David Kreji each supplied two assists in the triumph.
New York's Henrik Lundqvist, after turning aside 45-of-48 shots in Thursday's 3-2 overtime loss, let in five goals on 32 attempts Sunday.
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