BOSTON — They began the season seven weeks ago as the leaders of the Celtics’ “Bench With Attitude.”

Marcus Smart and Marcus Morris, along with Terry Rozier and Aron Baynes, provided a change of pace in a tough and gritty second unit.

A quarter of the way into the season, though, alterations had to be made by the struggling Celtics, and Smart and Morris moved into the starting lineup.

The Celtics have put together three straight wins since Smart became a starter on Nov. 26 in New Orleans, joining Morris, who has started the past five games.

They have replaced Gordon Hayward and Jaylen Brown, joining Kyrie Irving, Jayson Tatum and Al Horford in the first group for wins over the Pelicans, Cleveland Cavaliers and Minnesota Timberwolves.

The Celtics appear to be on the right track heading into tonight’s game at home against the New York Knicks, and the presence of Smart and Morris with the starters has made a difference.

“Morris has been one of the more consistent guys this whole season,” said Tatum before practice at the Auerbach Center on Tuesday. “Smart is just someone who does a little bit of everything. It’s two tough guys and they’ve been playing really well.”

Coach Brad Stevens had to mix things up with Hayward trying to get rid of the rust on his game and with Brown struggling. Hayward has been making progress the past two weeks, scoring 30 points with nine rebounds and eight assists against the Timberwolves, while Brown has been out the past three games with a bruised tailbone.

Brown returned to practice on Tuesday and should play against the Knicks, but it is expected that Stevens will stick, at least for now, with Smart and Morris as starters.

“Those guys have brought us good versatility,” said Stevens.

Smart and Morris have been able to help set an aggressive tone right away as starters, and the Celtics have avoided getting into holes early in games.

“Just that energy, that spark, like the energizer bunny,” said Smart when asked what the duo brings. “We’re the guys that come in and kind of start things, get things going energy wise, defensive wise and just all around, the dirtiness of the game.

“I’m constantly telling these guys a lot of games we’re winning aren’t going to be pretty. You’ve got to be willing to get your nose bloody and get dirty to win these games.

“We’re just doing whatever we have to do for the team.

“Everybody’s playing with a little more attitude, a little more swagger we were missing. I think we’re getting our swagger back.”

That was missing as the Celtics stumbled out to a 10-10 start before the three-game winning streak.

They have four days off in between games this week, giving the Celtics time to work on their game before a favorable portion of the schedule arrives.

“Everybody’s not hanging their heads,” said Smart. “There’s a little bit more daylight in the locker room. It’s good to see everybody smiling.

“They couldn’t understand what was going on either. Everybody was trying to find a way to come up with wins. Nobody could find a solution. We were all upset, not at each other, but with the situation we were in.

“We’re playing more 48-minute games. That was our biggest problem. We’d start picking it up in the second half when we were down. These last couple of games we’ve been playing right from the start.”

Stevens knows the Celtics are far from being into a groove, realizing that three wins in a row are just a start.

“We have a long way to go,” he said. “We’ve done more good things recently. I feel a little bit better about us week to week, but we still have a long way to go.”

Said Tatum: “We’ve just been playing better. Everybody individually is doing better. There’s a lot of different reasons (for the struggles). Maybe we believed the hype too much. We have a big target on our back and teams are coming after us and maybe we didn’t understand that fully. Nothing we can do about the past.”

The rough start, they hope, is going to be buried in the past with continued improvement in December.

“It’s funny because if you don’t humble yourself, the world has a way of humbling it for you,” said Smart. “For us to go through what we’ve been going through, it’s something that we needed and it brought us back to reality.”

Around the rim: Brown, who was hurt against the Dallas Mavericks on Nov. 24, went through an individual workout on Monday and practiced with the team on Tuesday. “I’m good. I’m ready to go,” said Brown. “I’m feeling better every day. Just looking forward to being there on Thursday and keeping this win streak going.” ... The Knicks will be without guard Trey Burke when they visit the TD Garden on Thursday. Burke, who has a ligament sprain in his knee, had 29 points and 11 assists off the bench when the Knicks stunned the Celtics at the Garden two weeks ago. ... The four-day break this week is the second-longest stretch without a game this season. The Celtics will be off seven straight days at the All-Star break in February.