San Antonio has won the last two games after dropping the opener.
Denver held a 25-22 lead after the first quarter, but trailed, 43-40, at the half.
San Antonio salted the contest away after Duncan made three of his five blocked shots in the fourth quarter.
Carmelo Anthony led Denver with 28 points and 12 rebounds. Allen Iverson had 20 points and four assists; Nene Hilario had 18 points and seven rebounds; while reserve J.R. Smith added 12 points and three rebounds for the Nuggets, who won the opener, 95-89, last Sunday.