Carmelo Anthony scored 33 points and Denver twice converted four-point plays to beat the Heat 112-105 Tuesday night.
The Nuggets' point total was a season high, and they outscored Miami 54-36 in the paint.
"We can't stop anybody right now," Heat coach Pat Riley said.
The defending NBA champions fell to 3-4 with their second consecutive loss, both at home.
Anthony lost his scoring duel with fellow 2003 draft pick Dwyane Wade, who had 37 points, 11 assists and eight rebounds. But the Nuggets reached .500 by winning their third in a row after an 0-3 start.
"A week ago the media had us buried," coach George Karl said. "Now we're good."
The Heat were again without Shaquille O'Neal because of a hyperextended left knee, his second injury to the knee this season. His status is day to day.
"If he wants to stay in Miami when they come to Denver in December, that would be good," Karl said.
Miami is also without starting guard Jason Williams, still recovering from offseason knee surgery. He might return Friday.
"Right now we have to almost be perfect to win," Riley said.
Thanks to fouls on Gary Payton, the Nuggets converted a pair of four-point plays in the second quarter. J.R. Smith sank a 3-pointer, was fouled and made the free throw. Andre Miller was fouled attempting a 3-pointer and made all three free throws, which were coupled with another free throw when Payton drew a technical for protesting the call.
Miller had a season-high 29 points, 10 assists and eight rebounds for the Nuggets. They missed 21 of 27 3-pointers, but Anthony did plenty of damage inside and shot 13-for-26.
"I get up for every game -- some games even a little more than others," Anthony said with a smile. "It's always fun playing against Dwyane and Miami, the champions."
An 11-0 run beginning late in the third quarter put the Nuggets ahead to stay. Reggie Evans' basket made it 84-83, and Earl Boykins made a 3-pointer -- his first basket after eight misses -- for an 89-83 lead.
Soon the margin was 95-85.
"It's that one dead spot for us," Wade said. "We had one bad stretch, and they went up 10 points on us."
Miami cut a 12-point deficit in half in the final minutes with consecutive 3-pointers by Wade and Antoine Walker. But the Nuggets sank six successive free throws down the stretch.
"We played our best offense and best defense in the fourth quarter," Karl said.
The Heat, who began the game last in the league in scoring, missed 10 of their first 11 shots to fall behind 19-4. They rallied and took their first lead at 25-24 on a 3-pointer by Walker.
Miami hit 3-pointers on its final three shots of the first half -- two by Wade, one by James Posey -- to lead 52-48.
The Heat surge included back-to-back dunks. When the 5-foot-5 Boykins entered the game for Denver, 6-foot-8 Dorell Wright immediately posted up on him for an easy alley-oop score. Udonis Haslem caught an alley-oop pass on a fast break for another dunk on the Heat's next possession.
But Miami faded at the finish and fell to 2-3 at home.
"We can't get them back," Haslem said. "They're gone now. We have no excuse. We're not playing well, and we know it."
- Nuggets F Nene, sidelined since Friday with a bruised knee, was inactive.
- The Nuggets led at the start of the final period for the first time this season.