Ahmad Bradshaw rushed for two touchdowns as New York (8-6) remained a game behind Dallas for the final NFC playoff spot.
The Redskins (4-10) were embarrassed by New York's defense, which recorded five sacks and picked off three Washington passes.
Manning completed 19-of-26 passes, connecting with Mario Manningham, Steve Smith and Derek Hagan for touchdowns, while Bradshaw carried the ball nine time for 61 yards.
The Redskins' Jason Campbell passed for 192 yards with a touchdown and two interceptions.
The Giants need wins in their final two games against Carolina and Minnesota and at least one Dallas loss to make the playoffs.
Celebrity Families of 2014 [PHOTOS]