J.R. Smith contributed 19 points while Raymond Felton supplied 16 and seven rebounds for second-seeded New York, which broke the contest open with a strong third period during which they outscored the Celtics 32-11.
Boston was led by Paul Pierce with 18 points, six rebounds and six assists.
Kevin Garnett donated 12 points and 11 boards for the Celtics, who will host Friday's Game 3.
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