Boston Coach Joe Mazzulla argues with referee Rodney Mott in the second half of Game 1 of the Eastern Conference Finals in Boston on Wednesday night. Center is forward Grant Williams. Charles Krupa/Associated Press

BOSTON — The expectations for a Boston Celtics title run are evident around TD Garden. The most visible reminder has to be the big, bold billboard plastered outside the building that reads: “Unfinished Business.”

The message evokes the memory of how the Celtics came two wins short of a championship a year ago. Adding even more emphasis: Two of the letters within the slogan are designed to look like a “1” and an “8.”

There are also obvious reminders that the Celtics are chasing the franchise’s 18th championship banner with a rookie head coach. It comes up when Joe Mazzulla gets face time with a national audience, as he did Wednesday when TNT announcer Kevin Harlan served up the in-game coaching interview with the introduction: ” … The youngest head coach in the NBA.”

Mostly, however, the indicators of Mazzulla’s inexperience emerge every time Boston takes a step back in its title pursuit, as it did by dropping Wednesday’s opening game of the Eastern Conference finals to the eighth-seeded Miami Heat.

Mazzulla, 34, inherited a championship-ready team, but not the accompanying respect. His decisions get dissected and, worse, second-guessed. Even by some of the paying customers, who plead from their seats for him to call a timeout – a favorite gripe that hangs over Mazzulla, and one he seems done with talking about.

But since the Celtics lost 123-116 Wednesday night, largely due to a third-quarter collapse in which they surrendered 46 points, Mazzulla couldn’t escape his least favorite topic. After the game, reporters asked variations of the same question. Pretty much: hey rookie, why didn’t you do anything to break up the Heat’s 21-12 run until the near the midway point of the quarter?

“Get better shots, don’t turn it over, and don’t foul, don’t give up offensive rebounds and don’t give up 3s,” Mazzulla said, choosing to answer literally a question about what could have been done to stop the run.

And when asked how he balances letting the game play out versus calling a timeout, Mazzulla, clearly annoyed, responded tersely while dodging the query.

“I called two in the first quarter,” Mazzulla chirped.

For the fourth time this postseason, the second-seeded Celtics lost at home. Mazzulla didn’t turn the ball over multiple times in the final quarter, like all-NBA player Jayson Tatum. And though he didn’t personally allow the Heat to shoot 51.6 percent from the arc (16 of 31), he will shoulder the majority of criticism for the Game 1 setback. Such is the life of a rookie head coach who was given one of the best teams in the NBA – and also the pressure of not messing it all up.

We all know the story by now. Mazzulla shouldn’t even be in this position. Last year when Ime Udoka, himself a rookie head coach at the time, formed the Celtics into a championship-caliber team, Mazzulla was an assistant stationed behind the bench. Last October, however, the team suspended Udoka for having an improper relationship with a team employee, and promoted the little-known coach from Rhode Island. The regular season went smoothly – the Celtics won 57 games and Mazzulla finished third in voting for the league’s Coach of the Year honor.

The intense young coach practices jujitsu, plays prison-style ball with his coaching staff and, allegedly, watches “The Town” four times a week – charming stories, though it was all the wins that helped build Mazzulla’s credibility. Those wins also made people forget, or not care, that Mazzulla prefers to give his veteran team the freedom to figure things out. The Celtics have two of the top 15 players in the league in Tatum and Jaylen Brown, along with Marcus Smart, last season’s defensive player of the year, and Marcus Brogdon, this season’s sixth man of the year. Also: Robert Williams III, the lob threat and paint protector, and the respected O.G. of the bunch, Al Horford.

The team is stacked, and Mazzulla has been smart enough to stay out the way, declining to call timeouts when his players hit rough patches. Even when he does stop the action, Mazzulla doesn’t appear to dominate a huddle. At times on Wednesday, despite being allotted 3 minutes and 30 seconds in a timeout, Mazzulla would keep it moving, spending as little as 15 seconds actually addressing players on the sideline.

However, even that brief amount of communication would have been greeted with applause had Mazzulla called for time as Boston’s nine-point halftime lead dwindled away. He chose, instead, to wait until the 6:28 mark. The lead had vanished while Miami seized control of the third quarter, and ultimately the game. During that timeout, Mazzulla tossed his clipboard and walked away from the huddle.

“Joe is real big on a lot of times not bailing us out on stuff when we’re playing like (expletive). So, we’ve got to look ourselves in the mirror. Joe can call a timeout, and then what, we come out and do the same thing? It’s on us,” Smart said. “Joe and his coaching staff, they put in a lot of work to come up with a game plan and put us in the right spots to succeed, but they’re not out there playing. We’ve got to come together and we’ve got to start helping each other out on both ends.”

After the game, Heat Coach Erik Spoelstra could sit down in peace. He wasn’t asked about his timeout usage. He didn’t face a single pointed question from the media about lulls in his team’s performance. No second guessing whatsoever.

This tranquility, of course, had everything to do with his team winning on the road. His postgame media session was so easy, so full of respect that at one point, a reporter even attempted to ask Spoelstra about the potential of becoming only the second eight seed to make the NBA Finals – though the Heat still have the arduous task of winning three more times for that scenario to play out.

Across the back corridors of the arena, where the coach of the home team sat and stewed, there were no inquiries about the upcoming Finals.

Mazzulla, whose curt and defensive responses to reporters’ questions have not helped his cause, faced another interrogation about his choices and his coaching style. Following that media session, Mazzulla walked out, grabbed his backpack, a to-go box of fruit and walked down the hallway with his wife. For a few minutes, at least, the only questions he confronted were inside his own head.