BOSTON — Kevin Garnett’s lack of composure didn’t lead to a loss. Miami’s did.

Boston’s emotional leader was slapped with two technicals after he elbowed Quentin Richardson in the jaw with 40 seconds left in the Celtics’ 85-76 victory over the Heat in their NBA playoff opener Saturday night.

Garnett faces a possible suspension and could miss the second game Tuesday night in Boston.

He said he was concerned that Paul Pierce, who had fallen in front of the Miami bench, had hurt his shoulder and wanted to clear space around him. Richardson came by and said something and Garnett struck him on the left side of the face with his left elbow.

“I was just concerned about Paul. You make your bed, you have to lay in it,” Garnett said about a possible suspension. “I am smarter than that. I have to keep my composure in a situation like that.”

The Heat’s loss of composure lasted much longer.

Leading 61-47 with 7:02 left in the third quarter, they fell behind 71-68 with three minutes gone in the fourth. They finished with 22 turnovers for 38 Boston points.

“The damage for us was done long before (the skirmish),” Miami Coach Erik Spoelstra said. “We just did not show a lot of composure. … To play to that kind of pressure, a little bit of duress, a little bit of adversity, we did not respond well to it.”

Before his ejection, Garnett had played well, with 15 points and nine rebounds. One of the NBA’s noted trash talkers, he found himself in the middle of a swarm of Heat players when Pierce fell down. There was shoving and technicals were called at first against Miami’s Udonis Haslim and Boston’s Glen Davis.

Then Garnett and Richardson got into it with Jermaine O’Neal nearby.

“I was trying to get over there to take the ball out of bounds,” Richardson said. “I said to Jermaine, ‘He (Pierce) is OK,’ because I knew nobody touched him. Is he taking a break like he does so many times?”

Dwyane Wade had a simple explanation: “We’re in the playoffs, that’s all. Just a couple of basketball players acting tough.”

Trailing 44-41 at halftime, the Celtics held the Heat to 32 points in the second half. And with substitute guard Tony Allen shadowing Wade, the Heat star scored 26 points after averaging 33.7 in three regular-season games against Boston.

“Tony and Baby (Davis) I thought, defensively, changed the game for us,” Celtics Coach Doc Rivers said.

Allen also scored a playoff career-high 14 points, and Pierce led Boston with 16. Richardson added 15 for Miami.

Miami allowed the second- fewest points in the regular season, an average of 94.2, but was outscored 21-10 in the fourth.

Garnett had a big game after missing last year’s playoffs because of a knee injury that required offseason surgery. Saturday’s playoff game was his first since Game 6 of the 2008 NBA finals, a 131-92 win over the Los Angeles Lakers for Boston’s 17th NBA championship. In that finale, he had 26 points, 14 rebounds, four assists, three steals, a block and no turnovers.

This year, both teams stressed that the playoffs were a new season and what happened before didn’t matter.

Boston won after going 3-7 in its last 10 games. Miami lost after going 12-1 in its final 13 games and 8-0 in its last eight games on the road.

“When you get Game 1 at home, you don’t find yourself back pedaling and pressuring yourself to go out on the road and win,” Pierce said.

Trailing by two starting the final quarter, the Celtics made it 68-68 on two free throws by Rajon Rondo, who had 10 points and 10 assists.

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