Arizona scored 13 fourth-quarter points as it rallied from a 21-6 deficit, and was in position to steal a win after recovering an on-side kickoff.
Washington quarterback Jason Campbell struggled while completing 12 of 18 passes for just 95 yards, no touchdowns and one interception.
Running back Clinton Portis scored twice on 18 attempts for 43 yards, and linebacker London Fletcher returned a pass interception 27 yards for a second-quarter touchdown as the Redskins (4-2) won their second game in a row.
Arizona's Kurt Warner, playing despite a left elbow injury, went 27-for-41 for 282 yards with two touchdowns and two interceptions.
2014: The Year in Music [PHOTOS]