Boston Celtics guard Isaiah Thomas, left, pushes against Washington Wizards guard John Wall during the first half of Game 6 of an NBA basketball second-round playoff series Friday, May 12, 2017, in Washington.

WASHINGTON — John Wall hit a 3-pointer with 3.5 seconds left for the go-ahead basket, then hopped atop the scorer’s table and yelled to celebrate at the conclusion of the Washington Wizards’ 92-91 victory over the Boston Celtics on Friday night that pushed their Eastern Conference semifinal to a Game 7.

Wall overcame a 1-for-12 start to finish with 26 points, and Bradley Beal led the Wizards with 33. The backcourt mates combined for 23 of Washington’s 26 points in the back-and-forth fourth quarter.

Isaiah Thomas and the Celtics showed up dressed in black, but couldn’t back up the fashion statement, blowing an 87-82 lead over the last two minutes. Thomas’ heave at the buzzer clanked off the rim. He and Avery Bradley each had 27 points.

Game 7 is at Boston on Monday night. The winner will face LeBron James and the Cleveland Cavaliers in the East finals starting Wednesday.

The host has won all 10 games between the Wizards and Celtics this season — four in the regular season and six in the playoffs.

Boston, which won Game 5 at home by 22 points, led Game 6 by 69-66 entering the fourth quarter, when a relatively blah game became much more compelling. The final period was tight throughout, featuring six ties and nine lead changes.

After Bradley and Beal traded shots to even it at 89, the Celtics had the ball and, coming out of a timeout with 14.1 seconds remaining, Al Horford made a 16-foot bank shot for the lead. After another timeout, Wall made the 3 that would decide the outcome. When the buzzer sounded, he ran to a corner of the court, then made his way to the sideline, jumped up and yelled and popped his jersey.

The Celtics got off to a terrible start, going 4 for 17 in the first quarter and not making a field goal over the final 5½ minutes or so. But Washington could not take full advantage, leading only 22-17 after that period.

And Boston kept right on missing in the second period, allowing Washington to open its biggest lead at 40-30. But some defensive lapses by the Wizards followed, and the Celtics scored the next 10 points en route to going up 42-41 at halftime.

Surprisingly, given that this was a potential playoff elimination game and an 8 p.m. tipoff on a Friday, there were plenty of empty seats around the arena at the outset.

Still, the fans made themselves heard, rising with loud support, for example, when Wizards substitute Kelly Oubre Jr. went in late in the first quarter — and booing when Celtics reserve Kelly Olynyk entered shortly thereafter. Oubre heard obscene chants directed his way in Boston after getting ejected from Game 3, then suspended, for shoving Olynyk after a pick.

That was one of the most memorable moments from this series, which also included Thomas getting a tooth knocked out in Game 1 and producing a 53-point outburst in Game 2, then a 26-0 run by Washington in Game 4.

Now everyone will find out what Game 7 has in store.

TIP-INS

Celtics: Their halftime lead was the visitors’ first since edge since 2-0 on Horford’s basket. … Trying to reach the East finals for the first time since 2012.

Wizards: Had lost seven consecutive elimination games at home. … Last reached the Eastern Conference finals in 1979. … This was the first win by a home team facing elimination on its court in these NBA playoffs. … F Otto Porter Jr. had zero points.

BACK IN BLACK

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.” Both coaches joked about the topic pregame. Asked about his players’ sartorial selections — and his own choice of a white shirt — Boston’s Brad Stevens said: “I’m not on the text chain. By design.”

Washington’s Scott Brooks said with a smile: “Wearing black, it’s great. It’s a great color. Makes me look thin, right?”