BOSTON — As fans started leaving TD Garden midway through the fourth quarter of a stunning Boston Celtics loss to the Philadelphia 76ers on Tuesday night, the words they were murmuring in the aisles and the concourses were “last year.”

As in the 2022 NBA playoffs — in this same second round against a potent Milwaukee Bucks team — when the Celtics dropped a very disappointing Game 5 at home in a 2-2 series and were facing a daunting task of going on the road to avoid elimination in Game 6.

Then Jayson Tatum had one of the best games of his life, scoring 46 points with unstoppable force to lead the Celtics to a punch-back win against the Bucks that changed the course of the series.

After the 76ers finished off their 115-103 Game 5 victory — in which they were never seriously threatened in the second half on Tuesday — the fans naturally drifted toward the positive thoughts of last year’s team-defining win in Milwaukee.

As for the prospect of needing to win a Game 7 to get out of this series now that Boston is down 3-2, that isn’t uncharted, either. Go right back to those words, “last year.” The 2022 Celtics won two Game 7s to get through the Eastern Conference playoffs including grabbing the rarest of gems, a Game 7 road win in Miami.

So this, naturally, is what the Celtics fans in coping with disappointment were clinging to. Except …

“Last year,” said Celtics guard Jaylen Brown. “is over with.”

Simple and profound.

This series has laid bare just how different the Celtics are from last year’s team that came two wins shy of winning its 18th championship. Almost all of the faces are the same.The ones that are different, namely Malcolm Brogdon, have been terrific additions; all he did was win Sixth Man of the Year.

But they are not the same.

It would be unfair and unwise to believe the Celtics could not run it back and win the next two games, it is also a mistake to make the assumption the 2023 playoff Celtics are mirrors of the 2022 version.

This year’s Celtics have different priorities, much of it coming from the styles of their coaches. Last season Ime Udoka generally focused on defense first and made lineup and strategy decisions to back it up.

For example, Udoka often played defensive specialist big men Al Horford and Robert Williams together. Horford is a strong on-ball big man defender. Williams is one of the best weakside shot blockers the league has seen in the past decade and is especially dangerous when he is allowed to roam free as a safety-style protector.

Udoka also had an affinity for hard-nosed wing defender Grant Williams, who played nearly 30 minutes a game in the playoffs last season and was often a primary defender for great opposing scorers.

The Celtics had the second-best defense of all the playoff teams last year. Sure, Tatum was the difference in that season-saving Game 6 in Milwaukee. But the Celtics held the Bucks to just 88 points per game on 40% shooting in winning Games 6 and 7. When they beat the Heat in Game 7 on the road to reach the Finals, they allowed 96 points on 42% shooting.

That was then.

First-year coach Joe Mazzulla was on Udoka’s coaching staff but has a different view. He tends to focus on offense and makes decisions that lean that way.

For example, the Robert Williams-Horford pairing is largely a thing of the past and hasn’t been seen against Joel Embiid and the 76ers. Grant Williams’ minutes have been reduced in half as Mazzulla prefers to play more offensive-first players like Brogdan.

The Celtics have three players who got votes for the NBA’s All-Defensive team that was released Tuesday and Derrick White made the second team.

But the Celtics currently rank 10th among playoff teams in defense this year, a big drop from last season.

They also rank first in offense.

When Mazzulla analyzes his team’s performance it is often offense-focused.

“We shot more free throws (in Game 5), we shot more 3s,” Mazzulla said. “I thought we were getting relatively good looks. We missed 10 wide open 3s in the first half and if a few went in we would’ve felt a little different about ourselves.”

All season long, Mazzulla has focused on the math around 3-pointers. Shoot and make more than your opponent and you win. And he aligns his strategy to match.

The 2022-23 Celtics are a product of this world view. They are 34-2 this season when they make more than 40% of their 3-pointers, a remarkable and reductive statistic. In Game 5 when they needed it most, they were 9-of-33 from beyond the arc (27%) before a couple in garbage time boosted it to 32% for the night.

When they shoot below that magic 40% number they are 29-28, quite average. To win Game 6 and 7 again, average won’t do.

Mazzulla was asked after the loss about Joel Embiid’s 33 points and 11 trips to the foul line. He answered a defensive question with an offensive answer.

“A lot of that has to do with how you’re playing offense,” he said. “If you’re not playing offense and getting out and running and those (Embiid post ups) are hard to stop because then you’re deciding what you’re willing to give away.”

Let’s be clear, a lot of times the Celtics do make a ton of 3-pointers and crush their opponents with it. In Game 2, when they won by 34 points, they made 20 to Philadelphia’s six.

This could happen again. They have big-time scorers and streaky shooters from Tatum to Brown to Brogdon to White. They are a very potent team that was the favorite at Caesars Sportsbook to win the title as of tip off in Game 5 (they’re now fourth, behind the Nuggets, Lakers and 76ers).

But if they’re going to comeback and win this time it must be acknowledged, it won’t be like last year.