The Hornets led by as many as 13 points in the second quarter, but were overwhelmed during a stretch that spanned the third and fourth periods. Denver won its fourth straight and is tied with Oklahoma City for the best record in the Western Conference at 6-2.
After winning its first two games of the season, the Hornets have lost five in a row.
New Orleans owned a 63-54 lead when Gallinari's dunk began the Denver surge. The Nuggets scored the final eight points of the third period and the first 11 of the fourth to take a 73-63 advantage.
Gallinari finished with 23 points and six assists. Al Harrington added 14 points, Arron Afflalo had 13 and Ty Lawson 12.
New Orleans was led by Greivis Vasquez with 16 points.