Jayson Tatum misfired on a potential game-winning 3-point attempt with 3.2 seconds remaining in the second overtime, concluding a valiant effort by a Celtics team missing starters Kyrie Irving (sore left knee), Al Horford (illness) and Jaylen Brown (concussion).
The Celtics appeared on their way to victory both in the final seconds of regulation play and the first overtime.
After forcing a Wizards turnover on an inbounds play, Boston tied the game 115-all on a layup by Tatum with 3.1 seconds to go in the first overtime.
Tatum, fouled on the play, had a chance to put the Celtics ahead, but missed the free throw, sending the game to a second overtime.
The Celtics likewise were in good shape after Marcus Morris' 3-pointer put them up 103-99 with 44.5 seconds to play in regulation time.
But Tatum missed one of two free throws with 32.4 seconds to go, and Jodie Meeks converted a brilliant Porter assist into a game-tying hoop with 2.4 seconds remaining, forcing the first extra session.
Beal had a team-high nine assists to complement his 34 points for the Wizards, who were playing a 21st straight game without star guard John Wall.
Porter recorded an 18-point, 11-rebound double-double, and Markieff Morris, squaring off with his twin brother Marcus, added 20 points for the Wizards, who snapped a two-game losing streak.
Marcus Morris poured in a team-high 31 points for the Celtics, who lost for just the third time in their last nine games.
Terry Rozier had 21 points and nine assists, Tatum finished with 19 points and Greg Monroe compiled a 16-point, 10-rebound double-double for Boston, which will play eight of its next 10 games on the road.
The Celtics seemed well in command early on, bolting out to a 21-6 lead in the first six minutes of the game behind Marcus Morris' two 3-pointers.
The Wizards then spent the next 27 minutes chipping away at the deficit, which was 20 at one point. Washington rallied within 59-52 by halftime and completed its comeback on a floater by Tomas Satoransky that put it up 77-76 with 3:35 remaining in the third period.
--Field Level Media
Washington | Boston | |
Bradley Beal 34 | Scoring | Marcus Morris 31 |
Bradley Beal 9 | Assists | Terry Rozier 9 |
Ian Mahinmi 11 | Rebounds | Greg Monroe 10 |
Markieff Morris 6 | Free Throws Made | Marcus Morris 5 |
Otto Porter Jr. 3 | Steals | Shane Larkin 2 |
Marcin Gortat 2 | Blocks | Terry Rozier 3 |
Team | Points | FG% | 3PM-3PA | FTM-FTA | Assists | Rebounds | Blocks | Steals | Turnovers |
Washington | 125 | 47.4 | 12-32 | 21-28 | 29 | 52 | 6 | 10 | 20 |
Boston | 124 | 48.5 | 12-26 | 16-23 | 30 | 44 | 5 | 9 | 17 |