The 7-foot Nelson shot 12-for-14 from the field, 5-of-6 from the free throw line and had eight rebounds as Colorado State improved to 8-0 at home. Dwight Boatner added 16 points.
Erik Benzel and Rodney Billups led Denver (5-5) with 15 points each as the Pioneers lost its eighth straight in Fort Collins. Their last victory at CSU came on Jan. 6, 1979.
Nelson hit four straight shots and scored nine points in the opening four minutes of the second half as the Rams extended their lead to 49-37.
Denver stayed within striking distance and Benzel's made it 68-59 with a 3-pointer with 4:28 left.
Three-pointers by Andrew Carpenter and Benzel got it to 76-69 with 1:20 remaining before Boatner put the game out of reach with a steal and three free throws.
Billups, who had 13 points by halftime, hit an off balance jumper in the final seconds to pull to within 38-35 at the break, erasing a 12-0 lead the Rams had taken early in the half.
Colorado State shot 70 percent in the first half and cooled down to 46 percent in the last 20 minutes.