The Washington Wizards didn’t do much physically in just their third practice of the month Saturday ahead of their matchup against the Boston Celtics. Practice time has been scarce in February, with 16 games scheduled in 27 days, so Coach Scott Brooks used the rare session to get his team in line mentally. The Wizards watched film unrushed and talked through some of their immediately correctable defensive issues.

On Sunday against the Celtics, Washington’s mental preparation paid dividends with a 104-91 win in which the team’s defense made up for another so-so offensive outing, and the Wizards held all-star Jayson Tatum, averaging 26.6 points per game this season, to just six points.

It helped that the Wizards (7-17) had a rested Bradley Beal, a new starting lineup — their 17th this season — and an opponent that looked as if it limped all the way to Capital One Arena from Boston after a brutal Friday night loss to the six-win Detroit Pistons.

“We were just locked in, from the practice we had yesterday, coming in today,” said Beal, who sat out Friday’s loss to the New York Knicks for rest. “We knew who we were playing. We knew what was at stake. We could come out lackadaisical and be down 30 early, or we could be ready to go and battle from the jump.”

Washington chose Option B and played one of its best first quarters of the season with Moritz Wagner, usually a third-string center, and Garrison Mathews starting alongside usual starters Beal, Russell Westbrook and Rui Hachimura. Thanks in part to Wagner, probably the loudest player on the roster, it was easier to hear the Wizards on defense from tip-off than it has been all season inside a largely empty Capital One Arena.

They held a 12-point lead at halftime, with Boston’s offense looking anemic.

“Moe talks. He communicates. Sometimes you want him to be quiet at times, but I like that,” said Brooks, who gave Wagner the start simply to give the team a different look at center. “I like the fact that he’s always engaged — you hear him behind. Even when he’s not playing, he’s still on the bench talking. I think he impacted the game that way.”

Beal looked as if he had swallowed rocket fuel after three restful days and led five scorers in double figures with 35 points on 10-for-18 shooting overall. He was 11 for 11 from the foul line and added seven rebounds, five assists and two steals.

Hachimura added 15 points in what Brooks called one of his best games of the year because of his activity on defense. Westbrook had 13 points, nine rebounds and 11 assists.

Wagner had 11 points in his first start of the season and just the sixth in his two seasons with the Wizards.

After a week in which Washington players up and down the roster spoke about the need to take pride in individual defense, Wagner spoke about the role trust — in themselves and in each other — played in Sunday’s win.

“The start had a lot to do with it. Just not getting down in the first quarter — and I don’t even mean points. I just mean mentally, like, keep trusting each other,” Wagner said. “Keep being uplifted and engaged throughout the whole first half. And then, yeah, once you establish that trust, it’s easier to go into the second half, keep on going like that. We’ve got to be sure to have that defensive intensity every game.”

The Wizards’ defense did the yeoman’s work its once high-powered offense did at the beginning of the season.

Washington shot 39.8 percent overall and just 23.3 percent from three as its long-range shooting struggles continued, but the offense hummed anyway with some of the better ball movement deployed all season. The Wizards had 21 assists on 29 made baskets through three quarters and entered the fourth with a 22-point lead.

Boston (13-13) shot 35.6 percent overall and 25.7 percent from three. With Tatum wrapped up for 23 minutes, Jaylen Brown and Kemba Walker sustained the offense with 25 points apiece.

“I thought tonight we were just active,” Brooks said. “We got back in transition defense. That’s been an Achilles’ heel for a while now. We weren’t worried about hanging around, trying to get an offensive rebound. We were getting back and getting into our defensive stance. We talked about that. We walked through it yesterday.”

There was no talk of cracking cans of White Claw, as Brooks joked about after Washington’s stunning win against the Brooklyn Nets two weeks ago. The coach and his players were measured in their postgame video conferences with just seven victories to their name this season. More than that, the Wizards have posted back-to-back wins just once this season, Jan. 1 and 3.

They will get another chance Monday with John Wall, set to play his first game in Washington against the team he spent the first decade of his NBA career playing for, and the Houston Rockets coming to town.

“It’s a big boost, 100 percent," Beal said of the win. “On the other side, we still didn’t do a lot of things perfect. A lot of things we were messing up on the fly. But I think our effort is what saved us. ... We kind of showed our hand of what we were capable of doing, and now, like I’ve been saying the last couple games, it’s consistency. We’ve got to build on that. Definitely excited about getting a win against a great team, but we’ve got another one coming in tomorrow that we’ve got to get some get-back on.”

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