Washington scored for the first time since early in the second quarter on Kai Forbath's 48-yard field goal with 11:57 left in the quarter.
The Redskins' offense has gained 195 yards through three quarters, compared to Pittsburgh's 311 total yards.
The only touchdown of the game for Washington came on a fourth-down pass from Robert Griffin III to Santana Moss in the second quarter. Forbath's ensuing extra point was blocked.
Ben Roethlisberger and the Steelers have moved the ball well against the Redskins, scoring on all but one of their drives. Roethlisberger has thrown for 200 yards and three touchdowns.
The Steelers had a punt return touchdown negated by a penalty for an illegal block in the back, allowing Washington to remain within 18 points.
Washington has the ball inside Pittsburgh territory to begin the fourth quarter.