Chandler, who missed two months of the season because of a hip injury, converted off an assist from Andre Igoudala after LaMarcus Aldridge had tied the score 111-111 by sinking a pair of free throws with 32 seconds to play.
Chandler finished with 13 points and six rebounds. Ty Lawson led the Nuggets with 24 points and a dozen assists. Kenneth Faried added 21 points and 11 boards.
Denver won its sixth in a row and improved to 15-2 at home.
Aldridge scored 28 for the Blazers, who lost their third consecutive game. Nicolas Batum added 22.
Portland was held to 19 points in the third quarter but outscored Denver 23-18 in the fourth quarter to force overtime.