The Washington Wizards didn’t get flustered when they trailed by 18 points. The Boston Celtics couldn’t hold a big lead for the second straight game.

Trevor Ariza scored 27 points capped by a 3-pointer that highlighted a fourth-quarter run as the Wizards rallied for a 106-99 victory Saturday.

“We don’t let anything rattle us too much,” Ariza said. “We just play and chip away and know things are going to happen. It’s a long game. We know teams can go on runs. They went on a run and we did, too.”

After Jeff Green’s layup with 6:14 left gave the Celtics a 92-84 lead, they went nearly six minutes without a field goal. Meanwhile, the Wizards were going on a 14-1 run that Ariza started with a jumper from the right corner. John Wall had five of his 20 points in the surge, which was interrupted only by a free throw by Jared Sullinger that gave Boston a 93-91 lead with 3:39 remaining.

“It was just, `Ok. We fought back. Let’s get some stops here and keep going. Keep stepping on them and let’s runaway with this one,”‘ Ariza said.

Nene tied it with a short baseline jumper and Wall gave the Wizards their first lead, 95-93, with a 20-footer with 2:51 to go. Marcin Gortat then blocked Sullinger’s shot and Ariza hit his 3-pointer with 2:25 remaining to put Washington ahead 98-93.

The Celtics had led 32-14 early in the second quarter. But in the last six minutes of the game, they were outscored 22-7, committed four turnovers and had two shots blocked.

“They came out and punched us right in the face in the first quarter,” Washington coach Randy Wittman said, “but I never saw any downness from our guys.”

Avery Bradley, an outstanding defender, scored 18 of his 26 points for Boston in a span of 8:01 in the second half. He started with a layup with 4:01 left in the third quarter that gave the Celtics a 66-59 lead and ended with a jumper with 8:00 left in the fourth that made it 88-82. Bradley then went to the bench and the Wizards began their comeback.

“He had a good roll,” Boston coach Brad Stevens said. “His effectiveness on the offensive end is just going to continue to improve.”

Washington (12-13) won its third straight game, all on the road. It started the day in fourth place in the Southeast Division but has a better record than Boston (12-16), which entered the game in first place in the Atlantic Division.

Nene, Gortat and Kevin Seraphin scored 13 points each for the Wizards.

For the Celtics, Sullinger had 22 points and 11 rebounds and Green added 13 points.

Three days after squandering a 21-point lead and losing to Detroit 107-106, Boston wasted lost another big cushion.

“You have to stay focused,” Celtics guard Jordan Crawford said. “You’ve got to step on the pedal when you have them down.”

The Celtics led 51-44 at halftime and 62-53 five minutes into the third quarter. But Washington tied it at 74 on a 3-pointer by Martell Webster with 42 seconds left in the third quarter. Then the Celtics took a two-point lead on Bradley’s jumper from the top of the key with 3.9 seconds left in the period.

“Avery had an amazing second half,” Webster said, “but we were resilient on the defensive end.”

Boston got off to its second straight strong start and led 30-14 after one quarter. On Wednesday night, it outscored Detroit 42-23 in the first.

The Celtics scored the first seven points of the game, took a 22-8 lead on Sullinger’s 3-point play with 4:07 left in the period and finished it by scoring the last five points. A layup by Gerald Wallace gave the Celtics their biggest lead, 32-14.

Then Boston collapsed in the last six minutes.

“We settled a lot for shots,” Wallace said. “We had some bad turnovers.”

Notes: The Wizards had at least 30 points in each of the last three quarters after scoring 14 in the first. … The game was the opener of an NBA-NHL doubleheader at TD Garden. The Boston Bruins played the Buffalo Sabres at night.

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