Wizards guard Brandon Jennings is backed down by Celtics guard Marcus Smart during the first quarter of Boston’s 110-102 win. Jennings was involved in a dust-up with Celtics guard Terry Rozier later in the first half. (Maddie Meyer/Getty Images)

Something has snapped within the Washington Wizards’ slumbering defense. And not even a visit to an enemy’s turf could arouse it once again.

The Boston Celtics commandeered the glass and simply battered the Wizards in a 110-102 win Monday night. At the end of the regular season series the teams are even with two wins apiece, but Boston (45-26) has erected a 2½ -game lead over Washington (42-28) for second place in the Eastern Conference standings behind the Cleveland Cavaliers.

“A lot of things hurt us tonight, but that was definitely glaring — offensive rebounds,” Coach Scott Brooks said. “We made them miss, but you got to make sure you rebound the basketball. It’s always the finishing part of the defense, and 20 offensive rebounds [is] way too many.”

The Celtics overcame a subpar shooting night (42.6 percent) by dominating Washington 54-39 in rebounds. The Wizards also shot poorly (43 percent overall and 8 of 35 from beyond the arc), and though they cut a 20-point deficit down to six with less than two minutes to go in the fourth quarter, the night was just a continuance of the team’s defensive slippage since the all-star break.

In the previous 14 games since the break, the Wizards had yielded the fourth-highest points per game in the league and defended the three-point line worse than any other team.

“It’s offense and defense, it’s not just one thing,” Wizards guard Bradley Beal said of the team’s recent issues. “We got to figure it out, whatever it is.”

Inside TD Garden, the Celtics took advantage of the Wizards’ defensive weakness by shooting 40 percent from beyond the arc in their breakout second quarter. Boston outscored Washington 28-19 in the quarter but turned up the intensity after the score was tied at 37 with 8:07 to go in the half. That’s when the seeds of discontent bloomed once again.

The last time the teams met, on Jan. 24, Wizards players embraced the hate by wearing all black to the game. The apparent message: The Wizards were attending the Celtics’ funeral. But several weeks have passed since then, and Washington has shifted its focus over time to other matters — like the team’s inconsistent 8-7 stretch since the break and its regressive defense.

By Monday night, Beal calmed things down by disagreeing with a reporter’s assertion that a rivalry existed between the teams.

No rivalry, Beal said. Just another game, Brooks said. Move along, nothing to see here. But newly acquired guard Brandon Jennings had other ideas.

Early in the second quarter, Jennings, who was not on the Wizards’ roster during the three previous matchups with Boston, inserted himself into the maybe-so, maybe-not rivalry by getting under the skin of Celtics guard Terry Rozier. After Jennings drained a midrange jumper — he rediscovered his missing shot by scoring seven points in the first half — he immediately jumped into Rozier’s way before the inbounds pass, effectively bumping Rozier in the chest. The players collided again while jogging up the court before Rozier ended the nuisance by shoving Jennings to the floor.

Players gathered around the combatants, and Wizards coaches stepped onto the court to keep the peace. All the while, a sellout crowd of 18,624 chanted, “Let’s go Celtics!”

Boston would answer the call, snapping the 37-37 tie and sending the Wizards into a spiral that endured for the rest of the game. Following the double technical fouls on Jennings and Rozier and a personal foul against Jennings, the Celtics ripped off a 16-5 run and led 58-47 at halftime.

“I don’t understand how I got a foul call for that. That’s something new,” Jennings said. “But yeah, just competing. This is a team we might have to meet in the playoffs. So [we] want to set the bar now.”

Washington agitator Jae Crowder tormented the Wizards with an offensive rebound putback and later back-to-back three-pointers. Boston drained four three-pointers in the second quarter, while Washington’s cold snap from Saturday’s loss in Charlotte continued as the Wizards made only 1 of 10 threes in the pivotal frame.

“We just started to miss some shots there,” Wizards guard John Wall said. “They made some shots, a couple tough shots. They got a lot offensive rebounds that kept them in the game . . . that’s what hurt us.”

But inconsistent shooting alone didn’t doom the Wizards. The disparity in rebounding contributed as well. While Boston created multiple scoring opportunities by securing 12 offensive rebounds, Washington settled for one-shot possessions. Boston owned a 31-16 rebounding edge in the first half, and at one point Celtics reserve center Kelly Olynyk had come off the bench and grabbed more rebounds (seven) than the Wizards’ starters combined.

The onslaught continued. By the end of the third quarter, Boston had scored 92 points. In the final quarter, the Celtics remained comfortably ahead even as the Wizards chipped away at their lead. Beal led Washington with 19 points on 6-for-15 shooting, while Wall scored just 16 points and dished eight assists — the second straight game in which Wall and Beal both scored fewer than 20 points. Center Marcin Gortat, plagued with fouls, played less than 12 minutes and contributed four points and four rebounds.

Celtics guard Isaiah Thomas returned after missing two games with a bone bruise in his knee and led all scorers with 25 points.

“It’s not going to get any easier,” Beal said. “Our schedule gets tougher. We got to bear down and get some wins.”