It was 68-65 entering the fourth. With James and four backups on the court, the Heat needed only 2 minutes, 22 seconds to outscore Milwaukee 12-0 and stretch the lead to 80-65 ensuring the reigning NBA champions would take a 2-0 series lead into Game 3 on Thursday.
"We held court," Heat coach Erik Spoelstra said. "We protected it for two games. We did what we're supposed to do. And that's it."
Chris Bosh, Shane Battier and Chris Andersen all scored 10 points for the Heat. James' postseason streaks of 22 straight games with at least 20 points, and 16 straight games of at least 25 points, both came to an end.
Ultimately, none of that mattered.
"We didn't get into our game like we wanted to in that third quarter," James said. "But we went into the fourth with a [three-point] lead and we were able to jump on them."
Ersan Ilyasova scored 21 points for Milwaukee, which got 16 from Mike Dunleavy and 14 from Larry Sanders. The Bucks' starting guards, Brandon Jennings and Monta Ellis, combined for only 15 points after teaming up to score 48 in Game 1.
"It's a series," said Sanders, who had a sore right ankle after he collided with Battier in the fourth quarter. "We made progress this game."
They'll need to make more, and do it quickly. James has never lost in 10 previous series where his team takes a 2-0 lead, and Wade is 8-0 in that same situation.
"In the playoffs you've got to find different ways to win," Wade said. "No matter what everybody says on the outside, [Milwaukee] is a good team. They played us very well."
For about 46 minutes, the Bucks played them even.
It was that 12-0 run that was the difference in what finished as a 12-point game.
Andersen started it with a three-point play, James had a layup not long afterward and the Heat were starting to roll. Another basket by Andersen off a pass from Ray Allen made it 77-65, and James found Norris Cole for a 3-pointer that capped the flurry and made it 80-65.
Storylines Miami leads 2-0
R Reigning champion Miami takes a 2-0 series lead thanks to a 12-0 run in the fourth.
• Dwyane Wade leads with 21 points, and LeBron James adds 19.