Jaylen Brown was the sharpest of the sharpshooting Celtics in Game 2

Jaylen Brown finished with 24 points, 8 rebounds, and 3 assists on 9-of-17 shooting in Game 2, making four of his seven treys.Matthew J Lee/Globe staff

Having Marcus Smart and Al Horford back in the lineup was a game-changer for the Celtics, but of equal transformative measure was the presence of Jaylen Brown.

What’s that you say, Brown played in Game 1 of the Eastern Conference finals? Sure, but he was a Miami glitterati-like late arrival, not showing up until the fourth quarter after the game had veered into the gutter during a 39-14 third-quarter avalanche.

This time Brown was present and accounted for from the start, the igniter for Boston’s Big Two And 1 core of himself, Jayson Tatum, and Smart, which combined for 75 points. He set the tone for the Celtics’ shock-and-awe shooting night during which they drained 10 of their first 12 3-point attempts, splashing more than the nearby Atlantic Ocean.

Brown and the Celtics turned the tide in the first quarter and sent a message to Miami, handing the Heat their first home loss of these playoffs in humiliating fashion, a 127-102 basketball beatdown.

There’s a tendency in some circles to want to reduce Brown to Tatum’s sidekick. The Other Jay. But the Celtics’ strength is in numbers and boasting two sublime wing stars. Brown is not a mere sidekick, the Robin to Tatum’s Batman. He’s more like the Batman to Tatum’s Superman. He can carry his own cape, thank you very much. Thursday was a reminder.

Brown finished with 24 points, 8 rebounds, and 3 assists on 9-of-17 shooting while making four of his seven treys. He delivered 11 points in the first quarter, doing damage when Tatum was on the bench, saddled with foul trouble.

Without Brown’s opening act, you don’t get the starring roles of Smart, who landed one rebound short of a triple-double in a rapturous performance for Smartophiles, and Tatum, who scored a team-high 27 points.

Rewind to the first quarter when Game 2 was actually a contest and the Celtics actually trailed by 10 (18-8). It was Brown who calmly canned an 18-footer, triggering a 39-10 tidal wave that allowed the Celtics to leave South Florida with a split.

The tipping point came with 4:14 left in the first quarter when Tatum was whistled for a charge, his second personal foul, and the Celtics down, 18-15. When Tatum returned for the second quarter, his team was up, 35-24. The Celtics outscored the Heat, 20-6, with their best player enjoying the best seat in the house.

“Those guys played great in that first quarter, especially that second half of that first quarter,” said Tatum. “That’s just what we do. We pick up for one another, regardless if somebody is out or in foul trouble. Everybody can make the right play.”

Of the 20 points the Celtics scored after Tatum departed, Brown scored or assisted on 12. Plus, he generated the hockey assist on Smart’s only first-quarter basket, creating the 3-pointer by passing out of a double-team to Horford.

Brown drilled a three over Gabe Vincent to start the run. He drove and hit Payton Pritchard for a triple. He fed Grant Williams for a three out of a double-team. He capped the quarter by burying a 28-footer with 29.6 seconds left.

“Obviously, JB can do it all,” said Tatum. “So when he has the ball, more often than not, great things are going to happen. He was just real decisive and getting to his spots and just making the right play, obviously drawing a lot of attention out there. He did a great job making the right reads.”

The Celtics shot a sizzling 63.2 percent in that fateful first, and nobody was hotter than Brown. No. 7 connected on four of five shots and all three of his threes for 11 points, picking up where he left off in the fourth quarter of Game 1 when he scored 15 points on 4-of-5 shooting and 3 of 3 from three.

It shouldn’t be surprising because Brown is shooting 48.1 percent from the field and 40.2 percent from beyond the arc this postseason, both up from the regular season.

The Celtics squeezed Miami with boa constrictor-like defense, but it was Boston’s scorching shooting touch that put the Heat on their heels.

“The shot-making, that got us out of what we normally do,” said Miami coach Erik Spoelstra. “That’s what shot-making can do. If you start the game 9 for 11 from three, that will get you out of your habits pretty quickly.”

Jaylen Brown, right, connected with head coach Ime Udoka after he hit a 3-pointer in the first half of Game 2. Matthew J Lee/Globe staff

The Three is the thing for the Celtics, who’ve yet to lose back-to-back games this postseason. When they’re dialed in from long distance, the 3-point line becomes a party line. Brown splashed the Celtics’ first points of the night on a three off a fantastic find from Smart.

The Green weren’t gun-shy, drilling 12 of 19 threes (63.2 percent) in a 70-point first half and finishing 20 of 40. Miami allowed more 3-point attempts than any other team in the league during the regular season.

“Our guys kept making the right reads, Jaylen, Jayson, Marcus, kind of attacking downhill and making plays for us,” said Horford.

When the Celtics are whole with their starting five, they can shoot anyone into a hole.

They’re the only team in the playoffs to make 20 or more threes in three games, and 39.9 percent of their points have come via the three, the second-highest rate entering Friday, trailing only the Mavericks (43.5).

The Celtics’ 37.7 shooting percentage from three is the highest in the postseason of any team that has played beyond the first round.

“They made shots that they missed last game,” said Miami star Jimmy Butler. “It’s going to be hard to beat anybody when they shoot 50 percent from the field and 50 percent from the three.”

While Butler spent the night looking for offensive assistance, the Green were sharing the ball and the wealth.

The Celtics were like a church collection plate — everybody contributed.

But the Game 2 redemption started with Brown playing like a man possessed.