Pierce and James Jones were tagged with double technical fouls after a hard foul by Jones that Pierce took umbrage to with 7:59 remaining. Pierce got in Jones' face as referees separated them.
Referee Ed Malloy, who was in the middle of both calls, immediately tossed Pierce on the second infraction. The Heat led 86-74 at the time of Pierce's ejection.
The Heat never relinquished their lead, winning 99-90. They lead the series 1-0.
Pierce did not address reporters after the game, but the ejection generated plenty of postgame chatter.
"I thought both [fouls on Jones and Wade] were flagrant fouls, personally, and I don't think we should react to either one," said Celtics coach Doc Rivers. "I thought James Jones' was a clear flagrant, went right for the head and grabbed. And I thought Dwyane Wade's was an absolute flagrant. He was just trying to run through Paul. I told Paul, 'You still don't react.' I thought, as a whole, we were the retaliating team tonight. We were never the first-hit team. But I really thought both were absolutely flagrant fouls, they should have been called."
Crew chief Dan Crawford conducted an interview with a pool reporter following the game and explained Pierce's second technical, which appeared to be the more mild of the two infractions.
"It's what we call a verbal taunt," Crawford said. "He directed profanity towards Wade. And in the rulebook, that is a verbal taunt. And it just so happened to be Pierce's second technical foul."
Asked about the series that led to Pierce's ejection, Kevin Garnett said: "It wasn't something that escalated or I felt like that needed to be blown out of proportion. I thought Ed [Malloy] did that, but he made the best judgement that he felt and made the call. It's what it is. It's over."
Reserve forward Glen Davis was more succinct.
"A dirty shot," Davis said, adding, "We're awake. Most definitely we smell what's going on, the coffee is brewing. We'll be back Game 2 and it'll be a great game."
The first infraction could have left Pierce in line for a suspension if it was determined he attempted to head-butt Jones, but Crawford suggested that wasn't the call.
"The first technical foul [on Pierce], it was contact during a dead ball," said Crawford. "He approached Jones and got right in his face. There wasn't a head-butt, but he got right into his face after a hard foul."
Said Jones: "It was just one of those things where a foul happened and it's a very emotional roller coaster that we're playing on. He got a little emotional and we got into something that should have really been nothing. But it happens when you're on the stage.
"I was just trying to go for a wrap-up foul. Just to make sure he didn't get an 'and-one.' He's one of the best at finishing after contact, so in that situation, I wanted to make sure he got two free throws and nothing more."
The game was aired by ABC, and analysts Mark Jackson and Jeff Van Gundy both thought Pierce's ejection was not warranted.
"You can't toss him out," Jackson said on air.
"I don't think that he could have said anything that would warrant being thrown out of this game," Van Gundy said. "What does it matter? No one hears it. He's talking to Dwyane Wade. You're ruining the end of this game over something that doesn't need to be addressed like this."
Pierce, who finished with 19 points and seven rebounds on 6-of-14 shooting, is expected to address the media before Boston's offday practice on Monday. It was the second playoff ejection of his career, the other coming against the Indiana Pacers in 2005.
Chris Forsberg covers the Celtics for ESPNBoston.com. Information from The Associated Press was used in this report.