BOSTON — There is irony in the number zero. It represents the absence of something. But when it’s in the loss column, it tells a completely different story. One of makes, misses, strategic genius and dumb luck.

The Cleveland Cavaliers, the Boston Celtics and the entire NBA universe stared at that 15-0 record all week, knowing that zero wouldn’t last forever.

Before the evening began, Donovan Mitchell had come to terms with that inevitability. As excited as he was to take on the defending champions on their glowing green floor with a trip to the NBA Cup Finals in Las Vegas, he was looking forward to learning what lessons this night had in store for him and his team had. .

Wanting to see how much they’ve grown since their season ended at the TD Garden in May, they hired a new coach in Kenny Atkinson and reinvented the way they play offense. It felt like things had changed. Their track record has certainly hinted at that. This was the night to find out if it was true.

“At the end of the day, we’re not winning championships today or tomorrow,” Mitchell said. “So we just use it as building blocks, but also enjoy the ride.”

Mitchell admitted their game plan was always obvious. “It was myself, it was (Darius Garland), pick-and-roll, pick-and-roll, pick-and-roll.” It’s a different team under Atkinson. The principles consist of a litany of unconventional off-ball cuts based on a variety of factors, faster tempo and slightly more three-point volume. It takes bits and pieces of the Celtics, the Warriors and many other teams in recent history that have played with a sense of mystery.

“It’s not a fluke or anything,” Evan Mobley said of the Cavaliers’ 15-0 start. Mobley defends the net against Jayson Tatum. (Winslow Townson/Getty Images)

The tide that has roused Cleveland’s ships has been Evan Mobley, who has come into his own on offense in a variety of ways. The Cavs have looked like they were ready to make noise in the East in the past, but then continued to fall short. Now that Mobley has moved on, he felt a matchup with the Celtics was a chance to make a real statement.

“That we are a real contender. It’s not a fluke or anything,” Mobley said. “We come here to get wins and get better every day.”

The result was the best offensive rating in the NBA, and of course, undefeated. Well, until now. That zero in the loss column is gone. The last look they got was at the back of Jayson Tatum’s jersey as he sealed the Celtics victory on a free throw with 20 seconds left.

Although the game was close, it was a journey through the Cavs’ path from last spring to this fall. A dismal first half played into Boston’s hands, a thunderous response after halftime and ultimately falling just short. Although they were missing much of their supporting cast in Caris LeVert, Isaac Okoro and Dean Wade, Atkinson ultimately got 36 points off his bench.

The problem was that Cleveland didn’t quite play like their new selves early on, as Boston jumped out to a 17-point halftime lead. The upside was that Cleveland held Boston to its lowest three-point attempt percentage of the season, as 41 of Boston’s 86 shots (47.6 percent) came from deep. While Atkinson is the kind of coach who is willing to boost his team’s three-point ratio, he doesn’t want to push them out of their comfort zone.

“We have to be ourselves,” Atkinson said. “We can’t suddenly say, ‘Hey guys, let’s shoot 60 3s this half.’ It’s just our style of play.”

It’s hard to be themselves when Boston is playing at its best, but you’d expect more from an undefeated team walking into the building where their previous season ended. It’s not as simple as rent out the Celtics have their way. Even an undefeated team doesn’t have that much cache with the basketball gods. The Celtics just reminded the Cavs what it looks like when you flip a switch.

“They had playoff strength and physicality,” Atkinson said. “We had regular season strength and physicality.”

The Cavs were fixated on isolation and pick-and-roll, an ironic approach considering everything Mitchell said before the game about how losing to the Celtics in the playoffs helped them distance themselves from that style.

“We were just mismatch chasing too much,” Mobley said. “In the second half we started doing more random basketball and more of our brand of basketball. That’s why we came back.”

The Cavs came out of the locker room leaning into the unpredictability of their cutting system, which makes them such a tough offense to contain. That freed Mobley to go into attack mode and only focus on cross-matches in the post when they organically came his way. He finished with a season-high six assists and 22 points on 8-for-13 shooting.

That was a very different story than the postseason, where Mobley’s success was often the byproduct of Joe Mazzulla’s game plan. The Celtics coach applied defensive pressure on Cleveland’s guards to get the ball out of their hands, giving Mobley free throws at the rim to ensure he took twos while Boston took threes.

Mobley spent the summer reshaping his game to be more versatile, becoming a point guard of sorts for the Cavs at times and learning to create from anywhere on the floor. He didn’t know what to expect when Atkinson took over, but Mobley praised the coach for tailoring the offense to his growing skill set.

After the loss Tuesday, Atkinson said he made a strategic mistake by not leaning on Mobley’s post skills on the Celtics guards in the first half to keep the game closer.

“(Mobley) could penalize switches, so we’ll have to keep looking at that,” Atkinson said. “That will be the play-offs, with teams switching to him.”

Darius Garland drives into Derrick White in the third quarter. Garland had an off night against Boston, going 3-for-21 from the field and 0-for-6 from deep. (Winslow Townson/Getty Images)

It was a new moment for a Cavs franchise built on Mitchell and Garland running the offense. While they leaned on that too much early on, they were burned by the fact that Garland just didn’t have it in this game.

While the Celtics play just two games this week and have had plenty of time to rest, the Cavs haven’t enjoyed consecutive days off since the start of the season almost a month ago. With all those wins, someone was bound to have a bad night. That ended up being Garland, who shot a dismal 3-for-21 from the field and 0-for-6 from deep. Only Sam Merrill – who played the fewest minutes for the Cavs – scored fewer than Garland.

“I think he hit a wall tonight,” Atkinson said. ‘He won’t say that. I’ll say it. It’s part of the NBA. It’s a shame it happened tonight.”

Garland chalked it up to missing shots and not wanting to play the fatigue card, but this Celtics backcourt led by Jrue Holiday and Derrick White has had its numbers since May’s playoff series. Their contrasting blend of physicality, discipline on hesitant moves and the ability to change shots without making mistakes gives the Celtics an answer for every facet of Garland’s game.

Many Cavs players learned many lessons Tuesday night, but Garland will have to go back to the drawing board for the rematch in two weeks.

“They obviously do a number of different things to put you in difficult positions,” Atkinson said. “So we’ll just have to bench it and try to adjust our game as well.”

The Cavs can now forget that they are undefeated. It was never something they took for granted anyway. Mitchell said win, lose or draw (well, you can’t draw) this game would be a lesson for the future, not a judgment on who they are now.

Mitchell never expected it to be 15-0. Why would he? Why would anyone? He only saw glimpses of what the team could become, of what they are now. They are a team that can make it through the competition, but there are still obstacles ahead of them. Now it’s time to clear the first one.

“We’re just looking at this as another test. There will be no championship won tonight,” Mitchell said. “The most important thing is: how can we continue to improve?”

(Top photo of Jayson Tatum looking to pass against Donovan Mitchell: Winslow Townson/Getty Images)