The Heat, though, knew it would take time to jell.
"It's a feel-out process," James said. "When you have so many options, it's something I'm not accustomed to, having that many threats out on the court at the same time."
Celtics coach Doc Rivers is convinced the Heat will progress into a title contender.
"They're going to be great," he said.
Not yet, though. Wade and Bosh weren't even all that good on opening night.
Wade was limited to 13 points on 4-of-16 shooting and Bosh added eight points and eight rebounds. The trio combined for 15 of the Heat's 17 turnovers -- eight by James, six by Wade and one by Bosh. And Miami was outscored 16-9 in the first quarter.
"This is one of 82," said Wade, whose preseason action was limited to the first three minutes because of a strained right hamstring. "Sorry if everyone thought we were going to go 82-0. It just ain't happening."
James announced his intention to leave Cleveland for Miami, revealing "The Decision" on national television 110 days before the opener.
Tuesday's decision went to the Celtics behind 20 points from Ray Allen, 19 from Paul Pierce and 10 points and 10 rebounds from Kevin Garnett. Rajon Rondo had 17 assists, two more than Miami had as a team.
Shaquille O'Neal, James' teammate last season and a member with Wade of Miami's last championship team in 2006, had nine points and seven rebounds for Boston. The Big Shamroq was just another reason for all the excitement surrounding the game.
"I just said to Paul as we were coming in here," Garnett said after taking his seat at the postgame news conference. "I said, 'Are we in the Finals already?' You know, but it did have a lot of hype on it."
Boston led 45-30 at halftime, but Miami cut that to 63-57 after the third quarter behind James' 15 points in that period. A layup by James made it 83-80 with 1:10 left in the game. But Boston, which once led by 19, got the last five points on a 3-pointer by Allen and two free throws by Pierce.
James came back to the building where he lost the last game of his Cleveland career in Game 6 of the Eastern Conference semifinals, the second time in three seasons that the Celtics eliminated the Cavaliers. He then became a free agent after seven seasons with the Cavaliers and signed with the Heat, who were beaten by the Celtics in the first round of last season's playoffs.
Boston's Big Three won the championship in their first season together, 2007-08, and then made it to the seventh game of the NBA Finals last season before losing to the Lakers in Los Angeles.
O'Neal said the Celtics weren't making a statement that predictions of the Heat going to the Finals are misguided.
"We just wanted to come out and win our first game," he said. "We let you all worry about the hoopla and all of that."
Boston held Miami to nine points in the first quarter, the first time since March 15, 2009, at the Philadelphia 76ers that the Heat scored nine points or fewer in a period. The last time James' Cavaliers scored nine or fewer points in a quarter was Feb. 2, 2007, when they managed nine in the second against the Chicago Bulls.
Things got so bad for the Heat in the first half that O'Neal, a notoriously poor free-throw shooter, made the first two he tried as a Celtic. That boosted the lead to 41-22 with 2:13 left in the second quarter.
"I think everybody was just a little bit anxious and wanting to make it work so much," Miami coach Erik Spoelstra said.
Miami then got a brief burst, scoring six straight points to make it 41-28. The last basket in that surge was a dunk by James on a backward pass from Eddie House, whose steal started their two-on-none break.
That drew cheers from two Heat fans -- one wearing a T-shirt with James' name on the back and the other with a jersey bearing Wade's name -- but a fan wearing a green Celtics T-shirt yelled, "He's supposed to do that. That is not impressive."
It was considering how poorly the Heat shot in the first half against a quick, aggressive Celtics defense.
Miami missed 30 of its 41 shots, a paltry 26.8 percent. Boston went 17-for-38 (44.7 percent).
The Celtics lost Pierce with 4:32 left in the third period when he hit the floor and hurt his back as he was charged with a blocking foul on James, who made two shots and cut the lead to 55-45. Pierce returned with 10:43 left in the game with Boston ahead 64-57.
And he finished the scoring with his two free throws with 22 seconds to go.
"It was a big game. It was a fun game," Rivers said. "They're going to be a lot better when we see them again. And, hopefully, we are as well."
James' 31 points were the most by a Heat player in his debut, passing the 25 scored by Antoine Walker and Willie Burton. ... Among the Boston athletes watching from the stands were David Ortiz of the Red Sox and Wes Welker, Vince Wilfork, Deion Branch and Brandon Meriweather of the Patriots. ... Glen Davis had 13 points on 6-for-7 shooting and five rebounds in 29 minutes off Boston's bench. ... Bosh is 2-12 in Boston, the most losses he's had as a visitor against any team.
Thanasis dunks one down before the quarter ends
Thanasis Antetokounmpo gets a steal, then receives a pass from Donte DiVincenzo before dunking it down.
Murray bounces pass to Hartenstein for dunk
Jamal Murray throws a pass to Isaiah Hartenstein for a dunk vs. the Pacers.
LeBron, Durant draft their All-Star starters
Watch as LeBron James and Kevin Durant take turns picking starters for the 2021 NBA All-Star Game.