The Boston Celtics have gone a perfect 3-0 to begin their preseason and with two exhibitions left, the reigning champions have gone right back to work, almost as if they had never won the NBA Finals and captured their 18th Larry O’Brien Trophy.

That’s the way to go, right?

Putting aside the belated season debut of Kristaps Porzingis, the new-look Eastern Conference rosters and the Olympic shooting woes of Jayson Tatum, the Celtics have one factor that inherently plagues most championship teams: themselves. Falling content after reaching the mountaintop once is a realistic and applicable worry that’s kept Boston on its toes to keep the title defenders from falling on its own sword — even if it means treating every preseason exhibition like an in-season battle for the top seed.

Boston hosted the Sixers on Saturday night, without Paul George, Joel Embiid, Tyrese Maxey, Andre Drummond and Kyle Lowry among others, and gave Philadelphia head coach Nick Nurse hell for 48 minutes. In fact, by the time the first 12 minutes had come and gone, the Celtics tallied 40 points on the scoreboard and followed that thunderous first quarter with a 70-point first half to end the night long before the final buzzer sounded.

“One of the strengths of this team is regardless of who’s in or nor, we execute at a high level, we play effort and I think that’s the way that we try to hold each other accountable to that,” Celtics head coach Joe Mazzulla told reporters after the 139-89 Celtics win, as seen on NBC Sports Boston’s postgame coverage. “I enjoy coaching them and they work hard so I think it’s key to try to keep that.”

Even though Mazzulla released the starters on the Sixers, opportunities were in place for Boston’s reserves and newcomers to also make an impact.

Offseason signee Lonnie Walker IV played a team-high 25 minutes and scored nine points on 4-of-7 shooting from the field four rebounds, seven assists, two steals and a block, finishing the night a plus-27. It was Walker’s first chance to capitalize on extended minutes, yet the 25-year-old adjusted Boston’s playbook relatively easily and made a notable stride amid the ongoing battle to seize a roster spot before Opening Night.

“I’m really happy that I got some action today. I got my feet wet,” Walker told reporters, per CLNS Media. “… Made some good reads, did solid on the defensive end — I think I gotta pick that up as well and rebound. As far as just what I gotta provide for the team is just other ways to impact winning. It’s not just scoring. I think everyone knows I can score so it’s more of all the other little things and kind of bumping that to a whole other notch.”

Mazzulla’s influence and locker room trust have grown tremendously ever since the 35-year-old’s interim tag was removed halfway through debuting as head coach. Now, under new circumstances and as the team with the biggest target on its back, Mazzulla’s message, too, has readjusted quite a bit. Boston is still treating the upcoming campaign like the 29 teams that didn’t win the Finals. The chase isn’t any different just because the Celtics are the only team that’ll open their season by raising a banner or being presented with a championship ring. Boston is treating the year as if they never won, getting a head start to the mid-season form by treating the meaningless preseason like there’s something at stake. Although if you ask Mazzulla, there absolutely is.

“I think there’s a standard that’s been set by the people that have been here for a long time — the players,” Mazzulla said, per NBC Sports Boston. “And then we try to bring guys in that wanna uphold that. So it’s a credit to the locker room for setting that one for a long time and it’s a credit to the guys coming in that work to be a part of that.”

Boston’s final two preseason contests will come against the Toronto Raptors.