Boston appeared to have the game in control when Kendrick Perkins made a layup to give the Celtics a six-point advantage with 2:45 remaining. They did not score again.
Dirk Nowitzki cut the Dallas deficit to three with 2:21 to go by converting a 3-point play and Jason Terry hit two free throws with 54 seconds left to bring the Mavericks within one.
After Kevin Garnett missed a jumper with 7 seconds left for Boston, Nowitzki grabbed the rebound and it was his pass that set up Kidd for the key 3-pointer.
Rajon Rondo then turned the ball over for the Celtics and Nowitzki made two foul shots with 2 seconds left to account for the final score.
Nowitzki finished with 29 points, helping Dallas sweep the two-game season series with the Celtics. Boston lost at home for just the fourth time in 26 games this year.
Ray Allen scored 24 points for Boston. He made three 3-pointers, moving him to within five of equaling Reggie Miller's NBA career record of 2,560.