Miller scored Denver's last 10 points in regulation and got another big basket in OT. His jumper put the Nuggets ahead 106-104 with 42.9 seconds left. Miller then made a steal on Jrue Holiday's errant pass to seal the Nuggets' fourth consecutive win.
The Atlantic Division-leading Sixers lost for the first time at home. They had won nine of 10 overall and were 6-0 at the Wells Fargo Center.
Thaddeus Young scored 22 points and Evan Turner added 20 for the Sixers.
The injury-riddled Nuggets had five players score in double digits, including Arron Afflalo's 14 and Ty Lawson's 13.
Neither team had their starting center. Denver's Timofey Mozgov sat out because of a back strain. Philadelphia's Spencer Hawes didn't play because of a left Achilles strain. Neither player is expected to miss much time. The Nuggets also were missing guard Rudy Fernandez (right Achilles strain) for the second straight game.
Down 82-72 in the fourth quarter, the Sixers scored 13 in a row. Andre Iguodala went end-to-end and dunked. He followed that up with a put-back to give Philadelphia its first lead, 83-82, since the first half.
The teams went back and forth until a frantic final minute of regulation.
Miller hit a short jumper to give Denver a 94-93 lead with 35 seconds left. Holiday dribbled behind his back, crossed over and scored to make it 95-94. Miller answered with a tough runner against two defenders with 7.9 seconds remaining.
Iguodala got fouled going to the basket and made one of two free throws to tie it with 4 seconds to go. Miller missed a 3-pointer as time expired to send it into overtime.
But he made up for with the winning shot against his former team. Miller came to Philadelphia in the trade that sent Allen Iverson to Denver in Dec. 2006.
Trailing 41-31 in the second quarter, the Nuggets made their move when coach George Karl put his two point guards - Miller and Lawson - on the floor together. Miller started a 20-4 run with a 3-pointer. He hit another one that got the Nuggets within 43-41. Nene made a layup and hit a free throw to complete a three-point play as Denver took a 44-43 lead.
Miller made the play of the game while pressuring Elton Brand after the big man grabbed a defensive rebound. Miller pretended to get elbowed in the face, covered up and hit the floor. Brand got called for a foul and Miller quickly got up, cracking a smile as fans booed.
Lawson's driving layup with the clock running down sent the Nuggets to the locker room up 51-45.
The Sixers used a 9-2 run to pull within 69-67 late in the third. But the Nuggets got consecutive 3-pointers from Al Harrington and Corey Brewer. Another 3 by Afflalo gave Denver a 78-70 lead.
Led by their strong bench, the Sixers pulled ahead 28-19 lead after one quarter. Williams hit a jumper, Young followed with a 19-footer and Williams dropped in a 3-pointer.
Notes: NBA commissioner David Stern was in the crowd. Stern talked about the Sixers' resurgence before the game. "The 76ers announced their presence against the Heat in the playoffs last year. This is just a continuation of that. It's exciting," he said. Philadelphia lost to Miami in five games in the first round of the Eastern Conference playoffs last spring. ... The Sixers were off to their best home start since opening 10-0 in 2002-03. ... Iguodala's only basket until the fourth quarter was a highlight play. He spun around Afflalo and threw down a one-handed dunk during Denver's second-quarter run. ... Rookie Nikola Vucevic made his first start in place of Hawes. He scored just two points in 12 minutes. ... The Nuggets went 4:11 without a point in the fourth quarter.