The Ravens defense held the Redskins scoreless through three quarters and limited Washington to 254 yards of total offense for the game.
Fading Washington (7-6) has lost four of its last five games while the red-hot Ravens (9-4) won for the seventh time in eight games and face an AFC North showdown next Sunday with division leader Pittsburgh.
Baltimore managed just 281 yards of total offense but rushed for 147 yards to just 62 for the Redskins.
Ravens quarterback Joe Flacco finished the night 10-of-21 for 134 yards with one touchdown. LeRon McClain ran for 61 yards and a touchdown on 20 carries.
Jason Campbell completed 21-of-37 passes for 218 yards with a TD and two interceptions for the Redskins. Clinton Portis was held to 32 yards on 11 carries.
Baltimore held a 17-0 lead going into the fourth quarter after touchdowns by McClain and Reed and a 32-yard field goal by Matt Stover with 4:11 to play in the third quarter.
Washington got on the board with 13:40 to play after LaRon Landry's interception set up a 43-yard field goal by Shaun Suisham. Campbell followed up with a 5-yard TD pass to Antwaan Randle El with 11:27 left to make it 17-10 -- but Flacco put the game away with a 28-yard TD pass to Derrick Mason with 3:35 left, capping a 12-play, 83-yard drive.