Nowitzki scored 27 points despite tearing a finger tendon in his non-shooting hand, including 10 in the fourth quarter as he tried to keep his team close. But the Mavericks were held to an uncharacteristic 37.3 percent shooting for the game.
James scored 24 points, Wade had 22 with 10 rebounds and Bosh cooled down in the second half to score 19.
The Heat didn’t shoot much better — 38.8 percent for the game — but they were a little bit better in the second half, hitting at 41 percent as they jammed their foot on the pedal for some distance.
"We just needed to lock in," said James.
Punctuating the win was a no-doubt-about-it field goal: Wade, driving against Jason Kidd on the right side, floated an alley-oop that James slashed to grab on the left side of the basket, throwing it down for a thunderous dunk.
"It was a grind. We didn’t get into an offensive flow the entire game," said Heat coach Erik Spoelstra. "This was more of a defensive battle."
The three Heat stars were good on that side of the ball, too. Minutes before he found James for the alley-oop, Wade blocked Mavs forward Shawn Marion on a jumper, then hit a three-pointer on the left side that gave Miami an 82-73 lead with barely three minutes to play.
"Two-way player. That’s what we expect of him," said Spoelstra.
The Heat, who trailed by as many as eight points in the third quarter, went ahead by as many as 12 down the stretch.
Two other highlights came when James drove past Marion and split the lane for a dunk as he was fouled, turning it into a three-point play, and a rebound that Wade converted into a long pass to Bosh for a dunk.
Both plays gave the Heat a 10-point lead. And although the teams were close in most aspects on the stat sheet, Miami earned a 46-36 edge in rebounding, including a 16-6 margin on the offensive glass.
"We got to play better overall. We have to be opportunistic," said Mavs coach Rick Carlisle. "They were more opportunistic than we were. And that’s been one of the traits of our run."
"What really killed us were the offensive rebounds," said Nowitzki. "We were out of position a lot. Especially in the fourth quarter, there were two or three in a row. That really hurt us."
Nowitzki said he had an X-ray on his left hand, that nothing was broken but that he will need to wear a splint on the middle finger. He was injured while lunging to swipe the ball from Bosh late in the fourth quarter.
"I’ll be all right," he said. "It’s on my left hand."
The series is a rematch of the 2006 NBA Finals, when Wade and the Heat beat Nowitzki’s Mavericks in six games after falling behind 0-2 in the series. It was the only other time either franchise made the Finals.
Game 2 of this set is Thursday in Miami, and Spoelstra said his team is "already moving on." The Heat snapped a 10-game losing streak to Dallas that dated all the way back to the ’06 Finals.
The spell included both of their meetings this past season. Those losses — on November 27 and December 20 — were the only setbacks during a 22-2 run in the schedule that helped Miami erase the feeling of a slow start to the season.
The Heat had to overcome a slow start to this game.
Nowitzki scored 13 points in a tight first half and the Mavericks carried a 44-43 into the locker room after a slow-going 24 minutes for both teams on the offensive end.
There were nine lead changes and six ties in the half and neither team shot better than 39 percent.
Both teams shot just 28.6 percent in the first quarter, with the Mavs squeezing out a 17-16 edge heading into the second.
Kidd hit back-to-back three-pointers in the quarter to get Dallas within 13-11, while James knocked down a three to halt a two-minute Miami drought and put the Heat up by four.
The Mavs scored five straight points to end the quarter with the lead, then let it go early in the second on Bosh’s putback dunk.
Neither team led by more than three points the rest of the way until halftime and the Mavs remained in front after Mike Miller missed a three-point try at the buzzer.
James scored nine points in the third quarter, including a three-pointer at the buzzer that gave the Heat a 65-61 lead heading into the fourth. Earlier in the third, the Mavericks went ahead 51-43 on DeShawn Stevenson’s three-pointer — the largest lead by either team until that point.
Wade said James’ buzzer-beating three gave the team momentum.
"We all made plays down the stretch to help us win the ballgame," he said.
The two Heat-Mavericks series are the only NBA Finals since 1998 that didn’t feature either the Los Angeles Lakers or the San Antonio Spurs…The Heat beat all of their previous three opponents this postseason in five games: the 76ers in the first round, then the battle-tested Celtics, then the Derrick Rose-led Bulls to capture the Eastern Conference title…The Mavs beat the Trail Blazers in six games, swept the Lakers in four and ousted the upstart Thunder in five to win the Western Conference.