The Eastern Conference series goes to a Game Seven at Boston.
However, Wall's heroics would give the Wizards the win and send the series to a do or die game seven. Washington countered with Beal draining a shot from three-point range and Wall tying the game at 87-all by hitting two free throws with 41 seconds left.
Thomas finished this one with 27 points and 7 assists, while Avery Bradley once again performed very well with 27 points shooting 10 from 18 from the field.
Boston will have home advantage in Monday's decider, with the Cleveland Cavaliers awaiting the winners of the TD Garden clash.
The home team has won every game of the series so far.
Following the game, Isaiah Thomas downplayed the wearing of the black suits as it clearly backfired.
Boston head coach Brad Stevens proved why he's considered one of the most creative play callers in the National Basketball Association, setting up the flawless in-bound play that gave Celtics forward Al Horford an open jumper that gave Boston a 91-89 lead with seven seconds left. When I think of (Game 6) I don't think about John Wall's three going in.
Wizards vs Boston Game 7 is Monday / Into boxing as well?
Princess Charlotte's Second Birthday Marked With New Royal Photo
The princess' hair is longer than when we last saw her at Christmas, and she's got a dark-blue clip keeping it tidy to the side. For Princess Charlotte's first birthday past year , Kensington Palace released four pictures of the little girl.
Thomas made some big plays down the stretch of Game 6, but he also had a costly turnover and a blocked shot that allowed the Wizards to come back and win.
To win Game 7, the Wizards would prefer it doesn't come down to such a finish on the road.
Luckily for the Wizards, Beal couldn't reach the ball, and Wall did his job.
After quieting talk of a funeral on Friday with his game victor, Wall hopes to put final nail in the Celtics' coffin on Monday.
The Wizards have not been involved in a Game 7 since 1979 when they defeated the San Antonio Spurs in the Conference Finals, 107-105, from the now-defunct Capital Centre in Landover, Maryland. Had he not hit that shot, it would be the third time that he, Beal and Gortat would have lost in six games in the second round, and they surely would have felt like they were running in place. A lot of guys doubt us winning this game at home. When made aware of it, Beal, who had a game-high 33 points, did a double-take as Wall explained his actions.
Instead of 1.7 seconds to attempt a go-ahead shot at the buzzer, the Celtics should have had approximately one additional second for the opportunity, according to the league.
The Celtics' black clothing was a nod to what the Wizards did before a regular-season matchup in January that became known as the "Funeral Game".