No fantastic finish needed for the Boston Celtics this time. They simply spoiled Madison Square Garden’s postseason homecoming party right from the start. Paul Pierce scored 38 points, Ray Allen added 32, and Rajon Rondo had a Celtics’ playoff-record 20 assists as Boston beat the New York Knicks 113-96 on Friday night to take a 3-0 in their first-round playoff series.Rondo had 15 points and 11 rebounds for the Celtics, who pulled out two close games in Boston but never trailed in this one…