The Broncos trailed 21-14 after three quarters, but Manning uncorked three scoring strikes in the fourth and Denver pulled away.
The NFL's leading passer completed 30-for-44 passes for 354 yards, hooking up with Knowshon Moreno, Demaryius Thomas and Joel Dreessen on late TD tosses while overcoming three interceptions and lost a fumble.
The Broncos (7-1) used the triumph to stay within one game of Kansas City (8-0) in the AFC West.
Robert Griffin III managed to make good on 15-of-30 pass attempts for 132 yards, one touchdown and two interceptions for the Redskins (2-5).
Washington head Coach Mike Shanahan lost in his return to Denver, where he led the Broncos for 14 seasons and won two Super Bowls before being fired in 2008.
Notable deaths of 2014 [PHOTOS]