Danilo Gallinari added 25 points, including a key 3-pointer in the extra period. Ty Lawson had 24 points and 12 assists for the Nuggets, who are 2-0 in overtime this season.
Portland, which lost for the first time in six OT games this season, was led by LaMarcus Aldridge's 28 points. Nicolas Batum had 22 points, J.J. Hickson 19 and Damian Lillard 16.
Gallinari hit his third 3 of the game for an overtime lead but Aldridge responded with a turnaround jumper that tied it 109-all with 51.8 seconds left. Lawson then lobbed a pass to JaVale McGee for an alley-oop dunk.
The game was tied again when Aldridge hit both free throws after being fouled by McGee, setting the stage for the decisive shot by Chandler.
Playing his second game since returning from a hip injury that sidelined him for two months, Chandler got open in the corner and Andre Iguodala got the ball to him. Chandler caught it, immediately put up the shot and it swished through. Lillard missed a 3-point try with 3.2 seconds left and Lawson made one of two free throws for the final score.
After Wesley Matthews hit a 5-foot runner to pull the Trail Blazers to 89-86 with 5:13 left, the Nuggets scored six straight points, starting with a pair of free throws by Kenneth Faried, who had 21 points and 11 rebounds, to stretch their lead to 95-86.
Portland came right back, scoring 10 of 12 points and pulling to 97-96 on a layup by Aldridge.
Lawson shook free on a drive to the basket for a layup with 45.4 seconds remaining to push the Nuggets' advantage to three points.
But Matthews hit a tying 3-pointer with 32 seconds remaining in regulation. Shots by Iguodala and Lillard both were off the mark in the final moments of the fourth quarter, sending the game into overtime tied at 99.
Down by three points at halftime, the Nuggets used an 8-0 burst capped by Iguodala's fast-break layup to go in front 70-63 with 5:03 remaining in the third quarter. The Trail Blazers cut it to 74-73 when Batum hit a 20-foot jumper, but Corey Brewer connected on a 3-pointer and Lawson finished a fast break with a layup following a Portland turnover.
Andre Miller's putback just before the third-quarter buzzer gave the Nuggets an 81-76 lead going into the final period.
Portland opened with its highest-scoring first quarter of the season, though Denver stayed right with the Trail Blazers at 35-33.
After a driving layup by Lawson put the Nuggets in front 51-50, Hickson converted a three-point play and Aldridge hit a jumper to help the Trail Blazers lead 57-54 at halftime.
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