‘Unfinished business’ fuels these Celtics — even in the first round

ATLANTA — Joe Mazzulla had about two minutes to accomplish a lot.

It was during the first timeout of Sunday’s Game 4 at State Farm Arena — when the Boston Celtics took a three-point lead after Derrick White’s jump shot with 7:47 left in the first quarter and forced the Atlanta Hawks to call a timeout — when Go to Celtics coach Jaylen Brown and ask what he recognizes in the Hawks’ coverage.

Mazzulla then quickly turned his attention, and his anger, to White, angrily reminding him of the defensive assignment he had blown in those first few minutes of the game, looking down on him as he ran to his assistants for the final moments of game planning.

That’s the kind of constant, relentless focus Mazzulla and the Celtics say they’ll need this postseason if they’re going to recover from the pain of last year’s NBA Finals loss to the Golden State Warriors.

Boston managed to improve the details enough to beat the Hawks 129-121 and take a 3-1 series lead and return home for Tuesday’s Game 5. This was the Celtics’ first chance to respond to a loss in the postseason, testing resolve. The team spent all season building.

Friday’s Game 3 loss wasn’t as shocking to the system as last season’s Game 6 loss at home to the Miami Heat in the Eastern Conference Finals, which made Boston’s road to the Finals more difficult, but it was enough to remind the Celtics that if the 2017 Warriors , the 2016 Cleveland Cavaliers, the 2014 San Antonio Spurs, the 2012 Heat or any team that lost in the Finals experiences a similar redemption story and uses that memory to carry them to a championship the following year.

“At the beginning of the year [the Finals defeat] The fuel was there, it really got us going,” Celtics big man Al Horford told ESPN after Game 4. “We kind of got away from it a little bit. But now that we’re in the playoffs, we don’t address it as a group, but when we talk about it individually, it’s something that’s still there.”

The details the Celtics addressed in Game 4 were mainly rebounding — the Hawks dominated the boards 48-29 in Game 3 — and cleaning up a defense that allowed the Hawks to shoot 56% from the floor.

The answer, in addition to the added effort, was a rotation switch that saw Horford and Robert Williams III back on the floor together, the way they spent most of last season.

This year, the team wanted to play faster and chose to share the center position between the two. On Sunday, Williams followed up his five rebound performance with 15 boards in Game 3 to go with 13 points, two blocks and two steals in 22 minutes, 10 more than in Game 3. Horford grabbed 11 rebounds and turned Boston’s early throttling on the board. A 49-42 rebounding edge with a minor adjustment in Game 4.

“That’s what makes our group so versatile,” Horford said. “There will be some games where we have to play together, and some games where we’ll have four guards and a big. That’s the strength of our team.”

There is hardly any time for first-round self-congratulation. In fact, if last year taught the Celtics anything, it was that the intensity needs to increase as the playoffs continue. After last season, the Celtics believed they had gone in the opposite direction after sweeping Kevin Durant, Kyrie Irving and the Brooklyn Nets in an intense first-round series.

“It wasn’t a traditional 2-7 matchup,” Celtics forward Jayson Tatum said after Game 4.

“And I think against Game 1 [the] Milwaukee [Bucks] Last year we kicked our ass because it was a different series, a different team, more physical. It took us a game to adjust. And I think that kind of hurt us and made it more difficult for us.

“Never get too comfortable with a lead because every game is just as important. There were times last year where we kind of relaxed.”

Tatum’s Finals performance last season is probably a big part of his personal fuel. The Celtics’ leading scorer averaged 21.5 points per game on 36.7% shooting and committed 23 turnovers in those six games against Golden State.

He looked the part of a determined man Sunday, setting the tone defensively for his team, finishing with three blocked shots, including one on Hawks big man Clint Capela.

“We talk about it all the time, do whatever it takes,” Tatum said. “Sometimes it’s more rewarding than hitting my tough shots.

“Not to brag, but I do it a lot. But those blocks really make my teammates react, and it really gets us going.”

The Celtics designed t-shirts that displayed the phrase “Unfinished Business,” with the “is” in “unfinished” resembling the 18, as the Celtics’ quest for the 18th championship in team history.

It is a tactful reminder of a painful experience. But the Celtics don’t seem to need that graphic-T inspiration.

“You’re going to have moments where you’re down for a game or two, but you don’t let it spiral,” Boston forward Grant Williams told ESPN after Boston’s Game 3 loss.

“We’ve had this growth as a team, especially with previous experience. To be able to go to the finals, no matter who’s in the rotation — you have to have that perspective and approach that urgency.”