From there, Dallas was forced to foul.
Pierce sank one of two free throws and Vince Carter hit a 3-pointer with 10 seconds left to make it 111-110. Pierce hit another pair of foul shots and Collison hit two free throws before Pierce and Courtney Lee each made two.
Mayo hit a meaningless 3-pointer at the buzzer to make it a two-point final margin.
The Celtics never trailed, opening a six-point lead in the first quarter and leading by as many as 10 in the second before Dallas scored 8 of the last 11 points in the half to head into the break down just 48-43.
Boston opened a 14-point lead early in the third quarter before the Mavericks scored 10 of the next 12 points. After Rondo drove to the basket to give Boston a 78-70 lead with the first score of the fourth quarter, the Mavericks went on a 7-2 run — five of those points coming from Mayo — to make it a three-point game.
Notes: Mavericks F Dirk Nowitzki has not played since October surgery on his right knee. Coach Rick Carlisle says there is no timetable for his return. ... The Celtics leave for a Texas swing, starting in Houston on Friday followed by San Antonio on Saturday. ... Mayo, who is second in the NBA in 3-pointers, did not make one until early in the second half.