BOSTON — If there was any concern about how the Celtics finished the regular season, losing four of their final 11 games, which, believe it or not, matched their worst stretch of the year, they dispelled that notion in the first two minutes of their first-round series opener against the undermanned Miami Heat.

Even the TD Garden crowd showed up early to the Sunday afternoon affair.

Boston scored on its first six possessions, unleashing its arsenal. Jaylen Brown and Jrue Holiday drilled 3-pointers. Kristaps Porziņģis shot over smaller defenders from both mid-range and the post. Jayson Tatum drove for a layup. Brown dunked. It was 14-0 before you blinked and 114-94 by the time the doors closed.

"It was difficult for us to trick ourselves into maintaining this crazy mindset of winning every regular-season game after it passed a point, knowing that we had the real thing coming soon," Porziņģis said. "And I'm glad we came out the way we came out tonight, and we set the stage for the rest of our path."

The Heat, playing without Jimmy Butler and Terry Rozier, will be fortunate to get a game in this series, so long as Boston stays focused on its first step on a championship path. These Celtics have lapsed before, and it has cost them on their past two quests. They would be wise to quickly dispose of a weakened rival.

"They're going to look at us and say we can't win, because we don't have Jimmy," said Bam Adebayo, Miami's leading scorer (24 points). "You look at records, because we were in the play-in, and then you look at their record, but at the end of the day, you gotta play the game. You gotta go out there and compete. You can't say somebody's gonna win if you haven't played the game yet. From that standpoint, we know we're going into the game with people doubting us, people not believing in us, but the guys in that locker room believe, so as long as they and the coaching staff believe, we've always got a chance."

Forgive everyone outside of Miami, including the oddsmakers, for writing the Heat off after this one.

There were moments when it seemed the Celtics might toy with their food again. Miami cut its early 15-point deficit to 29-25, only for Boston to respond on a 19-5 run over the next four minutes. The Heat got no closer than 12 points in the second half, when the Celtics pushed their advantage to as many as 34.

The final 15 minutes were a conditioning exercise.

There was always the possibility the Celtics, who built a 14-game lead over the Eastern Conference and coasted after the All-Star break, found another gear — one beyond their historic net rating in the regular season. Hard to tell if this was it, since this version of the Heat were no match, but Boston's defense was on lock. Between Holiday and Derrick White, Miami's Tyler Herro — thrust into a premier playmaking role — had nowhere to go. He started 1-for-7 from the field and totaled 11 points. Nowhere near enough.

"They came out with intentions on putting a lot of pressure on him, whether it was on the ball with pick-and-rolls or off the ball with movement," Heat coach Erik Spoelstra said. "We have to come up with ways to shake him free and get him to strength zones within the context of what we do. That's the playoffs."

Good luck. Adebayo can cook for all the Celtics care. Of whom else are the Celtics afraid in Butler's absence?

"If you're not going to double me," Adebayo said of Boston's strategy, "I'm gonna try to go score."

"This is business," said Porziņģis, who drew the Adebayo assignment. "Of course, we want to stop him as much as possible, understanding that they're going to play through him all the time. He's going to be involved in all the situations. I don't care about him. I care about our team and what we're trying to achieve. This is not 1-on-1, me against Bam; this is Celtics vs. Heat, so we'll make sure that's our focus."

Miami's undrafted scrappers, Caleb Martin and Duncan Robinson, gained confidence in their 3-0 start to last season's Eastern Conference finals against Boston, but they did not look so tough without their lead bully. Instead, Martin's reckless attempt to undercut Tatum in the final minute reeked of desperation.

"It's playoff basketball," Tatum said. "It's a physical game, playing against a physical team. S***'s gonna happen. It's probably not the last time I'm going to get hit like that or fouled in this series. I wasn't hurt."

It would serve the Celtics well to use that skirmish and Miami's late-game spurt, which cut a 34-point deficit to 14 in the fourth quarter, as fuel to avoid letting this series extending any further than it has to.

"We have to take that moment when they started to make that comeback as that driving force going forward," said Porziņģis, manufacturing more motivation. "They can make shots. They can throw some punches back, too. And they're dangerous, too. We cannot take it for granted and be like, 'OK, we're just going to be able to walk past them.' Just maintaining that healthy edge is going to be very important."

Spoelstra will swear his Heat can stick to their principles, lean harder into their available core and call on the next men, but he can only turn to so many reserves before Boston's talent gap becomes a chasm. Sunday's starting lineup played more possessions for Miami in Friday's play-in win than it did all season.

"Boston controlled this game from the tip," Spoelstra said. "You have to give them credit. They won the big-muscle areas, definitely won the 3-point line and the majority of areas in between, including defense. They were into us, getting us out of our normal flow, so we have to do a much better job by Wednesday."

It feels worse when Boston's entire rotation contributes to a total of 22 3-pointers, including four from eighth man Sam Hauser, who entered halftime with more points than anyone on the Heat but Adebayo. Makes you wonder whether the Celtics can make healthier teams look as outgunned as they did Miami.