Boston Celtics’ Isaiah Thomas (4) goes up for a shot against Washington Wizards’ Otto Porter Jr. (22) during the second quarter of a second-round NBA playoff basketball game on Sunday, April, 30, 2017, in Boston.

BOSTON — Isaiah Thomas had 33 points and nine assists, and the Boston Celtics made 19 3-pointers to beat the Washington Wizards 123-111 Sunday and take a 1-0 lead in their Eastern Conference semifinal matchup.

Thomas played just a day after attending the funeral for his sister, who died in a car accident earlier this month outside of Tacoma, Washington.

Al Horford added 21 points, 10 rebounds and nine assists. Jae Crowder finished with 24 points.

The Wizards were more energetic at the outset, jumping out to a 16-0 advantage and leading by as many as 17 points. But the Celtics rallied in the second quarter with Thomas briefly sidelined after getting one of his two front teeth knocked out.

Bradley Beal led Washington with 27 points. John Wall added 20 points and 16 assists.

Washington starter Markieff Morris played just 11 minutes before leaving with a sprained left ankle in the second quarter.

A rivalry has been simmering between the teams since last year, when Boston swept the season series.

They split their four regular-season matchups this season, but each included intense moments.

Sunday’s matchup was played at just as high a level, with a frenzied pace at times and physical play underneath the basket.

After the Wizards’ early scoring flurry, Thomas lost his tooth in a collision, and initially played through it. He found his tooth during a timeout, but started the second quarter on the bench while getting it repositioned in the locker room.

His teammates went on a 13-2 run without him to cut into Washington’s lead.

Boston led by 15 at the end of the third before a 9-0 spurt by the Wizards to start the final period closed the gap.

Thomas arrived back in Boston early Sunday. It was the second cross-country trip for him since Chyna Thomas died in a car accident last month, the day before the Celtics opened their first-round series against Chicago.

The Celtics star flew with Boston president of basketball operations Danny Ainge and assistant coach Jerome Allen.

During player introductions, Thomas pointed to the TD Garden rafters when his name was called.

TIP-INS

Wizards: Shot 10 of 23 from 3-point line. … Morris turned his left ankle after landing on Horford’s foot after a made jumper. He stayed in the game to complete his three-point play, then checked out. … Washington shot 62 percent (16 for 26) in the first quarter. … Grabbed the first 12 rebounds of the game.

Celtics: Didn’t score their first field goal until 6:42 remained in the first quarter, on a layup by Avery Bradley. … Didn’t register their first rebound of the game until the 5:57 mark. … Kelly Olynyk has scored in double figures in three of his last four games, after doing so just twice in his first 11 career playoff games.