The Celtics blew a double-digit lead, and eventually fell to the Wizards 85-83.
Kevin Garnett scored a team-high 17 points on 7-13 shooting, while Ray Allen added 16. Allen was only able to connect on 6-15 shots from the field and 2-8 attempts from deep.
Rajon Rondo tallied 13 points and nine assists. Paul Pierce scored 12 points and grabbed eight rebounds, and Semih Erden recorded six points and 11 boards filling in for the injured Shaquille O'Neal.
For Washington, recent addition Rashard Lewis netted 18 points on 7-13 shooting and pulled down 11 rebounds. JaVale McGee and rookie stud John Wall netted 16 apiece.
The Celtics dropped 35 points in the opening frame, thanks in large part to Allen's 10 points, and led by 15 heading into the 2nd quarter. The Wizards were able to hold the C's to just 21 points in the 2nd and cut their deficit to just 10 at the break.
Washington continued to chip away at Boston's lead and would have entered the 4th quarter knotted 70-70, had Rondo not sunk a jumper with less than four seconds left in the frame.
With just over 2:30 left in the game, Wall got into the lane and finished at the rim to give Washington it's first lead of the entire game, 81-79. After Davis made a layup, Wall banked in a deep three-pointer to put the Wizards up by three.
Pierce then missed a jumper. After giving a ball fake, Blatche jumped into him, but the C's didn't get the call. Garnett did knock down a layup with 40.9 seconds left in regulation to bring Boston within one. Pierce got another chance to hit his trademark step back jumper in Boston's last possession, but clanked it off the back iron.
The loss drops Boston to 33-10, while the Wizards improve to 13-29. The Celtics return to action Tuesday night when the Cavaliers visit Beantown for a 7:30 matchup.