After leading by 18 at halftime, the Celtics were outscored by 15 in the third quarter and three in the fourth quarter as John Wall led a fierce Washington comeback.
However, it was the Celtics who were superior in the high-scoring extra session thanks to a game-winning layup from Gerald Wallace with 2.5 seconds remaining.
In the loss, Wall recorded his second-career triple-double with 28 points (9-of-29 shooting), 11 rebounds and 10 assists.
The real story, though, was the play of Jeff Green, who poured in a game-high 39 points on 14-of-26 shooting, including 8-of-16 from three, and pulled down nine rebounds.
And although Green carried the load, the Celtics wouldn't have been able to capture just their second win in their last 11 games had it not been for the outstanding performance of point guard Phil Pressey.
Filling in for Rajon Rondo—who was resting on the second night of a back-to-back—Pressey scored a career-high 20 points (5-of-6 from three) and dished out four assists before fouling out in overtime.
Jared Sullinger was big as well, scoring 14 points and grabbing 11 rebounds on a night when the Celtics shot 46 percent from the field and 44 percent from three.
Bradley Beal added 14 points on 7-of-16 shooting for the Wizards, but missed all four of his threes. As a team, the Wizards shot a meager 32 percent from beyond the arc, nailing 7 of their 32 attempts.
In total, six Wizards finished in double figures.