The Wizards forced overtime when Chris Singleton got free for a dunk to tie the game at 88-88 with nine seconds left. A missed jumper by Rajon Rondo at the buzzer meant the game was headed to overtime.
But the extra five minutes were decisively in Boston's favor, as it outscored Washington, 12-4.
Things seemed to be going in the direction of a Wizards win as they hit halftime with a 42-37 lead. However, Washington was outscored 30-22 in the third quarter and lost control of the game.
It was a big night for three Celtics veterans. Rondo had 18 points and 14 assists, Kevin Garnett finished with 20 points and 13 rebounds, and Paul Pierce had 15 points and 10 rebounds.