The Celtics’ biggest issues came roaring back in Game 7 — what now?.

The Miami Heat had absorbed all the Boston Celtics – and the loud crowd inside TD Garden – had thrown at them early in the fourth quarter of Monday’s Game 7 of the Eastern Conference playoffs. Miami’s postseason hero was about to deliver the fatal blow.

Butler got the matchup he’d been looking for all series: a switch with Celtics big man Robert Williams III paired up on him, and he climbed up for a step-back midrange jumper. Swish.

On the other end, Celtics forward Jaylen Brown made a drive to the basket, but Butler snuck in behind him and tipped the ball away.

It was fated to fall into the hands of Caleb Martin, who morphed into a cross between Stephen King and James Bond during the course of the series.

Curry and Kevin Durant – and he passed it ahead to Butler for a nonchalant two-handed slam and rim swing for good measure.

Celtics coach Joe Mazzulla had already arrived on the court to call a timeout.

There were just around 11 minutes left in Boston’s season, but the outcome was already decided. Fans who booed the Celtics as they trudged to the bench knew it, too.

Boston’s chances of returning to the NBA Finals and becoming the first club in league history to overcome a 3-0 deficit in a postseason series were dashed.

“We got punked,” Celtics forward Grant Williams told ESPN. “We didn’t play our game from start to finish. Defensively, we just lost it all. And then offensively, we were scrambled and trying to do everything ourselves and just didn’t go our way.

“You hate to have that be the end of your season, especially with the fight that we’ve shown.”

A short while after Butler’s dagger, the Heat celebrated a 103-84 victory, sending the franchise back to the Finals for a second time in four seasons — both at the expense of the Celtics. That Miami did make history — the Heat became the first team to advance out of the play-in tournament and reach the Finals — was of little consequence to anyone inside the arena.

Instead, the overwhelming feeling was of an opportunity lost. The Celtics’ slogan for this year’s postseason run — Unfinished Business — played off their trip to the 2022 Finals, falling two wins short of a title, and the organization’s focus to get one step further.

But rather than finishing their business, the Celtics are now headed into a summer of soul-searching, unpacking what went wrong and what it will take to fix it.

Year 1 of the Celtics’ surprising coaching change
“I just didn’t have them ready to play.”

Those were the first eight words of Mazzulla’s press conference following the Celtics’ humiliation in Game 3 of the Eastern Conference finals.

Mazzulla sheltering his players was not unexpected. Throughout the season, he had gone out of his way to avoid taking shots at his teammates, a habit that had only intensified during the playoffs. It was also the latest illustration of Mazzulla’s significant shift in coaching approaches over the course of the season.

Mazzulla, the NBA’s youngest coach at 34, was an assistant on Ime Udoka’s staff last season before being catapulted into the team’s leadership role just three days before the season began.

Udoka was suspended for several infractions of team rules throughout the regular season.

On media day, Mazzulla stated that he aimed to keep the formula that worked under Udoka, which resulted in Boston reaching the Finals for the first time since 2010.

“It’s not about carrying on from just one person,” Mazzulla explained. “It’s about preserving our players’ identities.” So we had our challenges early in the season, but at our best, we knew who we were. It started with our defensive buy-in, and then it was about sharing the ball and moving swiftly on offense.

“So as much as we can stick to the things we were great at last year, and then find areas to improve along the way, I think is the right way to go.”

The differences between Mazzulla’s and Udoka’s approach quickly became clear.

Udoka, throughout his one season in Boston, would offer blunt assessments of his players to the media. Udoka blasted his team for a lack of mental toughness in January 2022 after Boston blew its fourth lead of at least 19 points that season.

The same could be said for Boston’s on-court approach. Udoka typically leaned on bigger, stronger, more defensive-oriented lineups. The pairing of Al Horford and Robert Williams became a lineup staple, and the bruising Grant Williams was the team’s lead reserve.

This season, Mazzulla has focused on smaller, faster lines with more shooting. After Robert Williams underwent knee surgery soon before training camp, the Horford-Williams combination didn’t see the court until late in the second round against the Philadelphia 76ers, with Mazzulla electing to start Derrick White instead. Grant Williams came and went in Boston’s rotation, with Mazzulla opting for summer acquisition Malcolm Brogdon to provide a more dynamic offensive threat.

“The 3-point attempt rate is the most important stat in the game of basketball,” Mazzulla remarked after a March defeat to the Brooklyn Nets, describing his approach to the game in part, “because of the pace of play, because of shot selection, and because of the shot selection.”

Mazzulla, on the other hand, prefers to start Derric with the capacity to go on runs.”Mazzulla instead preferring to start Derric of the ability to go on runs.”

Boston was exposed in the playoffs. The Celtics fell to 10th in defensive efficiency among playoff teams, continuing to struggle with the inconsistency that plagued them throughout their run to the Finals last season. The three losses to Miami at TD Garden in this series brought Boston’s home record to 11-12 during the previous two playoffs, the most home losses in NBA playoff history over a two-year stretch.

Late-game execution was an issue throughout the playoffs, especially in the first two games against the Heat, when Boston committed four errors inside the final three minutes and went on two long scoreless streaks. (Boston also let Game 5 against the Atlanta Hawks slip away at home and lost the season opener to Philadelphia.)

a game that Joel Embiid sat out with a knee injury.)

Boston was exposed in the postseason. The Celtics dropped to 10th in defensive efficiency among playoff teams, struggling with the inconsistent play that plagued them during their run to the Finals last season. The three losses to Miami at TD Garden in this series dropped Boston’s record to 11-12 at home over the past two playoffs, the most home losses over a two-year span in NBA playoff history.

Late-game execution was a problem throughout the playoffs, particularly in the first two games against the Heat, during which Boston committed multiple turnovers inside the final three minutes and had two long scoreless droughts down the stretch. (Boston also let Game 5 slip away at home against the Atlanta Hawks and dropped the opener to Philadelphia in a game that Joel Embiid sat out with a knee injury.)

“We just got to continue to put defense first,” Celtics guard Marcus Smart said after Game 7. “We were so bad on offense last year that that was a main focus for us this year. Unfortunately, our defense took a hit from it. We picked it back up, but it happens.”

Celtics players have praised Mazzulla for his performance throughout the season and did so again after Boston’s run came to a sudden halt.

“It was his first year; we got to [Game 7 of] the conference finals,” Jayson Tatum said of Mazzulla. “I don’t think people give him or us enough credit that, two days before the season starts, we find out we’re going to have a new coach. …

“Obviously, we wanted to win the championship. Didn’t happen. … But I think Joe did a great job this year.”

Boston likely runs it back, but massive star contracts loom

After struggling throughout the first 42 minutes of Game 6 of the conference semifinals, and with Boston trailing by two points to the Sixers in a contest it had to win to keep its season alive, Tatum suddenly turned his game — and, at the time, the Celtics’ season — around, hitting four 3-pointers and scoring 16 points in those final six minutes to lift Boston to a win.

“I’m one of the, humbly, one of the best basketball players in the world,” Tatum told ESPN’s Cassidy Hubbarth in the postgame on-court interview.

When Tatum then followed that performance with 51 points, setting a league record for the most points in a Game 7, it looked like it could be a storybook moment on the way to a title for Boston.

Then the series against Miami started. Tatum — who wore a T-shirt with “HUMBLY” splashed across to warm up for Game 2 — didn’t make a field goal in the fourth quarter of either of the first two games of the series before sitting the entire fourth quarter of the Heat’s blowout victory in Game 3.

After helping Boston claw its way back into the series with three straight wins, Tatum turned his ankle on the first play of Game 7 and never looked right after it. “It was frustrating to be a shell of myself,” Tatum said.

While Tatum’s injury and Boston’s poor shooting will be lingering reminders of why the Celtics lost Game 7, they were not to blame for the Celtics’ 3-0 deficit. Those issues have a familiar ring.

With open air space and a 10-point lead, Boston can look unbeatable. But that crispness often goes away in close games, replaced by frenetic play that creates both forced and unforced errors to fuel the opposition — like what happened in the final minutes of Game 6, only for Boston to be saved by White’s last-second putback.

And that goes back to the team’s best players, Tatum and Brown, who have now played in a combined 199 playoff games and who scored a combined 15 points on 15 shots in the fourth quarters of Games 1 and 2 then didn’t play in the final frame of Game 3 as Boston fell into too massive a hole to overcome.

Tatum struggled to 14 points on 5-for-13 shooting, while Brown had as many turnovers as made field goals in Game 7, finishing with 19 points on 8-for-23 shooting.

“Just a terrible game,” Brown said. “When my team needed me most … [Tatum] hurt his ankle, first play of the game, and you could see it swelling up on him. He couldn’t move out there. It was tough for him.

“My team turned to me to make plays, and I came up short. I failed. It’s tough.”

“I give credit to Miami,” he added, “but just a terrible job.”

This summer, Boston can offer Brown — after he made his second All-Star team and first All-NBA appearance — the richest deal in NBA history: a five-year, $295 million contract extension. (Had Brown not made All-NBA, he would’ve been eligible to sign a four-year, $189 million pact instead.)

And if either Brown or the Celtics are unwilling to agree to an extension, the Celtics will be in a position in which they could lose Brown as an unrestricted free agent for nothing next summer.

“I don’t even really know how to answer that question right now, to be honest,” Brown said when asked how he expects extension talks to play out. “Take it one day at a time, focus on getting better. Focus on what the future holds and see where we are from there.”

Assuming Brown agrees to a supermax extension, however, his future would be tied to Boston through the 2029 season, while Tatum — who by being named to a second straight All-NBA team qualified for his own five-year, $310 million extension next summer — is set to be under contract until the summer of 2030.

Under the league’s new collective bargaining agreement — one the Celtics ironically helped play an outsize role in getting done, considering Grant Williams, Brogdon and Brown are all on the National Basketball Players Association’s executive committee — having two players combining for more than $100 million per season could make team building difficult.

With the remainder of Boston’s core — Robert Williams, Smart, Horford, White and Brogdon — all under contract for at least the next two seasons, the Celtics are as well-equipped in the short term as any NBA team to compete for championships now.

The future of Grant Williams is murkier. After being a stalwart of Boston’s playoff run last year, his role fluctuated wildly under Mazzulla, including in these playoffs. Williams will be a restricted free agent this summer, giving the Celtics the ability to match any offer or move on via a sign-and-trade deal.

“Just focused on today. We planned on making it to the Finals, and it didn’t go that way,” Williams said.

“So I’ll figure [free agency] out when time comes.”

Boston’s championship window remains open. That’s always going to be the case when a roster features two of the league’s elite wing players who are entering their primes and will likely remain under contract through the rest of the decade.

But the past several seasons already feel, to some degree, like missed opportunities. Since Brown entered the NBA in 2016, the Celtics have played a league-leading 112 playoff games, the most by any team over a seven-year period in NBA history without winning a title. Their 61 playoff wins during that span are more than any team not named Golden State.

Over that same time frame, four teams — the Warriors (three), Toronto Raptors, Milwaukee Bucks and Los Angeles Lakers — have won championships, while the Heat and Cleveland Cavaliers have made multiple Finals appearances.

But the Celtics keep falling short, with Butler and Miami becoming the latest group to face them down when it matters most. That Boston pulled itself to the brink of the greatest escape in NBA history only adds to the misery.

As a result, instead of this battle-tested group finishing their business this season, the Celtics head into the offseason with no assurance they ever will.

“We’ve shown that we can get [to the Finals],” Tatum said. “S—, we got to the conference finals. It’s my fourth time in six years — been to the Finals once.

“We know we had a special opportunity this year. We just fell a little bit short. It’s not like we’re not capable [or] we don’t have the talent. We do. Just didn’t go our way this year.”