DALLAS -- The Boston Celtics readily admit that the aftermath of their championship celebration has impacted their intensity this season.

"We were a lion last season, and some games this year we've looked like a house cat," center Kristaps Porzingis said after the Celtics' 122-107 win Saturday over the Dallas Mavericks. "We want to have that spirit as a team this year, and it's tough. Obviously we can't trick ourselves and make it [like] it's playoffs every game. It's tough, just human nature. But we know the group that we have and we know that we're going to bring it to the big games, but we need to bring it consistently and keep building on top of good wins like tonight."

The Celtics, who won 68 games last regular season and lost only three times during the postseason run to the franchise's record-setting 18th title, are second in the Eastern Conference standings with a 32-14 record. Boston jumped to a 21-5 start but is only 11-9 since then and sit 4.5 games behind the Cavaliers.

"We're definitely working towards getting our killer instinct back," said Porzingis, who scored 18 points in Saturday's win, his first game at the American Airlines Center since the Mavs traded him to the Washington Wizards at the 2022 deadline. "We want to have that. Some moments we've looked really good, some moments not so good. Some moments we've cruised a little bit."

Boston arrived in Dallas off an embarrassing blowout loss to the Los Angeles Lakers on national television Thursday. There was a motivational quote written on the white board in the visitors' locker room that was attributed to star forward Jaylen Brown, although he didn't think that he actually uttered those particular words.

"Whatever it takes to inspire the team," Brown said.

Brown did, however, cite one of his favorite sayings that he believes applies to Boston's relative struggles this season: "Winter always turns to spring."

In this case, the saying reflects Brown's confidence that the Celtics will soon go on a dominant run. Boston hasn't had a winning streak longer than three games since November.

"It's coming. It's coming," said Brown, who had 22 points, 8 rebounds and 6 assists against the Mavs. "You just keep working. It's coming. You got to keep fighting if you want to be what you say you want to be, got to be tested and you got to pass those tests and be worthy of it. It's been hard. Shots are not going in. It's looked a little bit ugly at times. Our offense has been a little bit [off]. The energy hasn't been flowing the way it's used to, but that's all right.

"Just keep your mind, you keep your spirit lifted, you keep your teammates' spirit lifted and you come out and you play basketball, the tide will turn."