Jamaal Tinsley hacked Pierce on a drive to the basket late in the second quarter, and Pierce responded by scoring 13 of his 31 points in a three-minute span that broke things open in a 101-86 victory Tuesday night.
Boston remained unbeaten (6-0) and matched its best start since the 1987-88 season. The Celtics still are chasing their best start, 14 straight wins to begin the 1957-58 season.
"You've got to be playing very well to be 6-0," Indiana's Jermaine O'Neal said. "They have a very good team. Their supporting guys are doing very, very well. You've got to tip your hat off to those guys."
The game was tied at 38 when Tinsley fouled Pierce. Pierce quickly turned toward Tinsley, but kept his cool. Suddenly awakened, Pierce even did push-ups between free throws to taunt Tinsley and the crowd.
"I was just trying to blow off some steam, get my head back," he said. "That's all."
Boston coach Doc Rivers took advantage of the situation.
"Clearly, they lit a fire under Paul," Rivers said. "He thought the play was not a clean play. Got him upset, and as a coach, you've got to make a decision. Sometimes there, we went to [isolations] for Paul right away after that, and my read was if he gets going because of that, then we ride him."
Moments after Tinsley's foul, Pierce went baseline for a thunderous dunk. A Celtics player on the bench shouted, "Oops, you got him mad! Uh-oh!" Pierce fueled a 14-5 run that gave the Celtics a 52-43 lead at halftime.
Ray Allen picked up where Pierce left off. Scoreless in the first half, Allen had 15 of his 17 points in the third quarter. The Celtics led by as many as 16 in the period and took a 76-65 edge into the fourth quarter.
"I pick and choose my moments, and that's how the game shifted," Allen said. "As a scorer, you just allow the game to come to you, and you find your spots."
Indiana made a push late. Tinsley scored back-to-back buckets to cut Boston's lead to 89-82 with 4:06 to go, but Kevin Garnett made a long jumper on the other end to help the Celtics maintain control.
Garnett had 18 points and 11 rebounds, his sixth double-double in six games.
"Kevin is the glue of that team," O'Neal said. "Paul and Ray are very, very good players. I didn't have any doubt that these guys would be able to blend into a system, but emotionally, the energy comes from Kevin."
Boston outscored the Pacers 33-20 from the free throw line and held the Pacers to 35 percent shooting.
It took Boston until Dec. 9 last season to win its sixth game. By then, the Celtics had 13 losses. Boston has won by fewer than 10 points just once, a 98-95 overtime victory at Toronto.
"You saw me last year," Rivers said. "Did it look like we were having a lot of fun? Winning means fun.
"Even if at times our guys know we are a better team than what we show, when you like each other, and you're winning, that is fun."
Danny Granger led Indiana (3-4) with 24 points and seven rebounds, and O'Neal added 10 points and nine boards.
Indiana led by six points three times in the first quarter -- Boston's largest deficit of the season.
The Celtics appeared nonchalant through most of the first half and struggled to make shots. Their defense and their role players kept them in the game before Pierce got going.
"They are a terrific team," Indiana coach Jim O'Brien said. "I think they will surprise a lot of people with how good a defensive team they are. They're big, rangy and have excellent quickness."
It was O'Brien's first game against Boston as Indiana head coach. He led the Celtics to the Eastern Conference finals in 2002. ... Former Pacer Scot Pollard returned as a Celtic. He played three seasons for Indiana, and was one of the team's most popular players. He was cheered when he entered the game in the first quarter. He finished with five points and two rebounds in a season-high 11 minutes. ... Boston forwards Brian Scalabrine and James Posey returned to the lineup after missing Saturday's win at New Jersey with injuries. ... Tinsley was called for a flagrant foul 1 with 1:45 to go for shoving Rajon Rondo on a dunk attempt.
Kevin Love, LeBron James and Kyrie Irving combine for 71 points as the Cavaliers go up 31 points at the half and rout the Raptors 116-78.
After the Raptors' Game 5 loss to the Cavaliers, Stephen A. Smith has some harsh criticism for Toronto, saying, "It was one of the most pathetic performances that I've ever seen in my life."
The Cleveland Cavaliers vaporized the Toronto Raptors in Game 5, smothering the Canadian backcourt to take a 3-2 series lead in the East finals.