ATLANTA -- Joe Mazzulla had about two minutes to accomplish quite a bit.

It was during the first timeout of Sunday's Game 4 at State Farm Arena -- the Boston Celtics led by three points after Derrick White's jump shot with 7:47 remaining in the first quarter forced the Atlanta Hawks to request the break -- when the Celtics coach walked to Jaylen Brown to ask what he was recognizing in the Hawks' coverage.

Mazzulla then quickly turned his attention, and his ire, to White, angrily reminding him of a blown defensive assignment in those first few minutes of play, staring him down while rushing to his assistants for the final moments of game planning.

That's the kind of constant, relentless attention Mazzulla and the Celtics say they'll require this postseason if they're going to get over the pain of losing last year's NBA Finals to the Golden State Warriors.

Boston managed to improve upon enough fine details to beat the Hawks 129-121 and take a 3-1 series lead heading back home for Tuesday's Game 5. It was the Celtics' first opportunity this postseason to respond to a loss, testing the resolve the team had spent all season building.

Friday's Game 3 loss wasn't a shock to the system like last season's Game 6 home loss to the Miami Heat in the Eastern Conference finals, which made Boston's path to the Finals that much trickier, but it was enough to remind the Celtics of what it takes to experience a similar redemption story to the 2017 Warriors, 2016 Cleveland Cavaliers, 2014 San Antonio Spurs, 2012 Heat, or any team that lost in the Finals and used that memory to drive it to a championship the following year.

"Early in the year [the Finals defeat] was fuel, 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're not addressing 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 primarily 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, besides additional 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 spot between the two. Sunday, Williams followed his five-rebound performance in Game 3 with 15 boards to go with 13 points, two blocks and two steals in 22 minutes, 10 more than Game 3. Horford grabbed 11 rebounds, and Boston turned that previous throttling on the boards into a 49-42 rebounding edge in Game 4 with one minor adjustment.

"That's what makes our group so versatile," Horford said. "There's going to be some games where we have to play together, and some games that we'll have four guards and one big. That's the strength of our team."

The first round is hardly the time for self-congratulation. In fact, if last year taught the Celtics anything, it was that the intensity needs to escalate as the playoffs continue. Last postseason, the Celtics believed they went the opposite direction after sweeping Kevin Durant, Kyrie Irving and the Brooklyn Nets in an intense first-round series.

"That wasn't a traditional 2-7 matchup," Celtics forward Jayson Tatum said after Game 4. "We swept them, but ... that was the toughest sweep I've ever been a part of.

"And I think Game 1 against [the] Milwaukee [Bucks] last year we got our ass kicked 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 tougher for us.

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

Tatum's Finals performance last season likely remains a large 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 for his team defensively, finishing with three blocked shots, including one of Hawks big man Clint Capela.

"We talk about it all the time, just do whatever it takes," Tatum said. "Sometimes those are more rewarding than me hitting tough shots.

"Not to brag, but I do that a lot. But those blocks really get a reaction out of my teammates, and that really gets us going."

The Celtics designed T-shirts that display the phrase "unfinished business," with the "is" in "unfinished" stylized to resemble an 18, as in the Celtics' quest for an 18th championship in team history.

It's a gimmicky reminder of a painful experience. But the Celtics don't appear to require that graphic-T motivation.

"You're going to have moments where you let down for a game or two, but you can't let that spiral," Boston forward Grant Williams told ESPN after Boston's Game 3 loss.

"That's the growth we have to have as a team, especially with the prior experience. Being able to go to the Finals, no matter who was in the rotation -- you have to have that perspective and communicate that urgency."