0502 GMT July 24, 2021
Boston won the play-in contest on Tuesday to secure the seventh seed in the Eastern Conference playoffs, BBC wrote.
They will meet the second-seeded Brooklyn Nets in the first round, with game one scheduled for Saturday.
Washington has one more chance to make the postseason when it hosts the Indiana Pacers today.
The winner will secure the eighth and final spot in the Eastern Conference playoffs and face the top-seeded Philadelphia 76ers in the first round.
Washington led 56-55 in the opening minute of the third quarter before Boston, which lost five of its last six games in the regular season, scored 14 straight points during a 19-2 burst.
Tatum scored 23 of his 50 points in the third quarter while Kemba Walker added 29 points for the Celtics. Bradley Beal scored a team-high 22 for Washington.
The play-in tournament has been introduced on a one-year basis for the 2020-21 season, and will determine which teams take the seventh and eighth seeded positions in each conference for the playoffs.