While the Celtics’ win in Washington on Monday was dominant and never in doubt, it was not exactly complete.

The Celtics led by 33 entering the fourth quarter when Joe Mazzulla pulled his starters. But the bench submitted an ugly effort against the Wizards’ backups. They were outscored, 32-18, and committed eight turnovers. Their lead dwindled to as little as 15 with 1:33 to go, and while their victory was not threatened, the performance was still alarming.

So much so that on Tuesday, when they returned to Boston, Mazzulla called for a backups-only film session to go over what went wrong.

The message was clearly received. On Wednesday, faced with the same situation after the Celtics’ starters built a 38-point lead over the Pacers entering the fourth, the bench had an encouraging bounce-back effort. They erupted for 46 points – which marked the highest scoring final period in TD Garden history – as they pushed the lead to as big as 53. They didn’t commit a single turnover in a dominant final period.

In Tuesday’s session, Mazzulla preached ball security, rebounding, defending without fouling and staying organized offensively. After Wednesday’s performance, Mazzulla praised the unit for their purpose and the other areas they focused on.

“I thought we were just a lot more composed,” Lamar Stevens said. “You’ve got to go through things to learn and get better, and I felt like we responded by just taking care of the ball, being confident in the plays that we make, being confident in each other, and just going out and playing Celtics basketball. I thought we definitely responded from that Washington game for sure.”

Tuesday’s meeting seemed to be hugely beneficial. Hauser said Mazzulla talked about the unit’s roles and what he’s looking for in those situations and that “hearing that from him just brought a lot of clarity to all of us.” A meeting of that nature may seem atypical, but it was certainly welcomed.

“I wouldn’t say it’s unusual but it was cool to get the opportunity to do, for the head coach to take the time out to want to work with us and want us to be so attentive to the details, even down to whoever may be the last person on the bench,” Stevens said. “It’s just the way the Celtics play, who we are, and it’s just our identity, 1-15, so I think it’s just a great representation of who he is and who we’re trying to be as an organization.”

After an offseason that included trading some of their best bench options, there is some uncertainty about the team’s depth and roles to be carved out. And while the Celtics’ top six will take up the bulk of the playing time this season and ultimately be the most responsible in their championship pursuit, the bench’s play is still important. There will be nights throughout the year when the Celtics need a spark or some production from that unit.

If it wasn’t clear already, Tuesday’s film session drove the point home.

“I didn’t do it enough last year,” Mazzulla said of holding the session. “I think it’s another area of where I learned is before I became a coach, I spent all my time with those guys, and that was one of my favorite things to do because that unit has a hard job because everything is up in the air. They don’t know when they’re playing, when they’re getting their shots, who they’re playing against. Is it in a lead or is in a deficit? Is it in meaningful minutes or ones that don’t really matter? So they have a really hard job and I think the more we can be on the same page about their value regardless of what’s going on, I think it’s important for our team.

“We talked today. We got 14 games in 25 days, and there will be back-to-backs where people will be sitting and people will be missing games, and just have to have everybody ready. They take a lot of pride in their role in that.”

Another gear?

Kristaps Porzingis summed up what it was like to be on the court during the Celtics’ 155-point onslaught in Wednesday’s win.

“How did it feel? I barely like got (past) half court most of the time and we already were shooting and making it,” Porzingis said.

It was that easy for the Celtics, whose 155 points marked the second-biggest output in a regular-season game in franchise history. Through four games, they boast a league-best 124.8 offensive rating. The offense, despite the new additions, is already humming, but Porzingis claimed there’s another gear they can get to.

“We’re still building chemistry,” Porzingis said. “Even though we have some glimpses of really good plays and passes, we’re still building chemistry. I’m still still like catching up on the little nuances and little things that (Jayson Tatum) likes to do, that (Jaylen Brown) likes to do, and just still like figuring each other out, you know? It might look like it’s already really good because we’re just beating these teams easy but it’s gonna get much, much better.”

Mazzulla isn’t comfortable even though the offense looks great now. The Celtics’ offense also started last season at a historic pace, and it eventually, and naturally, cooled off. Mazzulla is already anticipating some lulls. The key is to make them brief.

“I think it’s trying to find small ways to reinvent them so that they seem new and fun,” Mazzulla said. “And at the same time, understand that when we’re at our best, we have to do these particular things. And so it’s early, we’ll go through a phase in the season where it’s a little bit stale, and we got to fight like hell to get out of it. And that’s just kind of how the season works. And it’s more about how quickly can we get out of those small, stale moments and get back to what makes us really good.”

Extra rest

Last season, Al Horford sat the second game of every back-to-back as the veteran got some extra rest before the playoffs. It’s expected that the 37-year-old Horford – who is now coming off the bench – will continue on that plan, but Mazzulla hasn’t confirmed that. The Celtics’ first back-to-back is next Friday and Saturday with home games against the Nets and Raptors.

“We haven’t talked about it yet, but I’m sure we’ll do what we can to make sure we win the game and give those guys a rest if they need,” Mazzulla said.