Jimmy Butler, the smiling villain, is dismantling the Boston Celtics in the NBA playoffs

MIAMI — For much of Game 3 of the NBA's Eastern Conference finals on Sunday, Jimmy Butler did something he does not often do: He played a supporting role. He created off the dribble, zipped passes to his Heat teammates for open shots and pushed to score only when the opportunity made too much sense not to seize it.

Butler could have easily tried to take over against the reeling Boston Celtics. But he has shaped the Heat in his no-quit, self-assured image, and empowered their cast of unsung players to lead. Then, shortly before halftime on Sunday, as if anyone needed to be reminded of his presence, Butler dribbled the ball upcourt and went straight at the Celtics' Grant Williams, his latest nemesis, for a jumper off the glass.

After drawing a foul on the shot for good measure, Butler fell to his back and stayed there for longer than was necessary — just so he could point at Williams and make it clear that he had made him look foolish, again.

"In all the moments of truth," Heat Coach Erik Spoelstra said, "Jimmy is going to put his will on the game."

Another game, another clinic given by Miami, whose 128-102 victory on Sunday was an end-to-end drubbing. The Heat, who have a 3-0 series lead, will go for the sweep at home on Tuesday, driven by their increasingly credible championship dreams as an eighth seed.

The Celtics' Jaylen Brown called the Game 3 loss "embarrassing." Boston Coach Joe Mazzulla took the blame. "I just didn't have them ready to play," he said.

All things considered, it was a muted performance by Butler, who finished with 16 points, 8 rebounds and 6 assists. But for the first time in the series, he faced traps. Both he and Bam Adebayo found teammates who were willing to help. Gabe Vincent scored 29 points, and Duncan Robinson finished with 22.

"Jimmy and Bam are fueling that," Spoelstra said. "They are just infusing those guys with confidence."

It would be easy to describe Butler as a showman, as someone who turns the court into a stage. He is not an impassive person. He emotes. He interacts with opposing players. He sings to himself. And he seems to delight in those moments (plural) when a crowded arena awaits his next act.

Make no mistake: There is a theatrical element to his approach, especially in the playoffs. It was on full display in Game 2 on Friday, after Williams connected on a 3-pointer to build on Boston's narrow lead midway through the fourth quarter. Williams began jawing with Butler on his way back up the court. On the ensuing possession, Butler scored on Williams and drew a foul. Afterward, Butler and Williams knocked foreheads as they continued their — how to put this delicately? — conversation.

"l like that," Butler said. "I'm all for that. It makes me key in a lot more. It pushes that will that I have to win a lot more. It makes me smile. When people talk to me, I'm like, OK, I know I'm a decent player if you want to talk to me out of everybody that you can talk to."

For Williams, talking to Butler was a miscalculation. The Heat closed that game with a 24-9 run. After the win, Butler strode to his news conference crooning along to "Somebody's Problem," a song by the country artist Morgan Wallen, which Butler was playing on his iPhone.

"It's a hit in the locker room right now," said Butler, who described himself as the team D.J. "So I get to pick and choose what we listen to."

The thing about Butler, though, is that all his extracurriculars — and all the attention that he draws to himself, whether intentional or not — are a means to an end. They motivate him, push him to perform. He is not brash for the sake of being brash. He is brash because being brash helps him win.

"He loves to win," said Mike Marquis, who was his coach at Tyler Junior College, a two-year school about 100 miles southeast of Dallas. "Some people hate to lose. He absolutely loves to win. I think sometimes there's a negative connotation with hating to lose, with bad sportsmanship and all that. But when I coached him, he didn't have any of that — he just loved to win."

Butler, who had a difficult childhood, was not highly recruited coming out of Tomball High School in Texas. He had a scholarship offer from Centenary, a small college in Louisiana that has since transitioned to Division III, and a partial offer from Quinnipiac. But Tyler, Butler said, was where he felt wanted.

Joe Fulce, a teammate of his at Tyler and later at Marquette, recalled that Butler had an uncanny ability to "curate his own world" whenever he played basketball. Outside the gym, there were problems and challenges. Inside the gym, the many distractions of his daily life somehow ceased to exist.

"That's hard as hell to do," Fulce said. "It's almost like he was a magician."

Marquis caught another glimpse of that single-minded focus when the N.B.A. concluded its 2019-20 season inside a spectator-free bubble at Walt Disney World because of the coronavirus pandemic. While other players were going stir crazy, Butler thrived in that sort of insulated environment, hauling the fifth-seeded Heat to the NBA finals before they lost to the Los Angeles Lakers in six games.

Today, Butler is one of the league's most recognizable players and a global pitchman for a low-calorie beer. But he still finds a way to close himself off from the world around him whenever he plays basketball, and he is not all that dissimilar to many of his teammates who were overlooked until they found success in Miami. The Heat have nine undrafted players on their roster, including Vincent and Robinson.

Butler went to junior college. He was the final pick of the first round of the 2011 NBA draft. Even this season, he was not selected as an All-Star (which, in hindsight, was probably an oversight). The veteran guard Kyle Lowry has said Butler is one of the most unselfish stars he has played with.

"He is us, and we are him," Spoelstra told reporters earlier in the postseason, as a way of explaining the synergy between Butler and the team around him. "Sometimes, the psychotic meets the psychotic."

Together, they are one win from the NBA finals.