The Saints and Indianapolis Colts (12-0), who topped Tennessee 27-17, are the only unbeaten teams in the NFL.
Meachem also scored on a 44-yard fumble return and Hartley kicked three other field goals, from 34, 28 and 27 yards.
Jason Campbell threw for 367 yards, the highest total of his career, and three touchdowns for Washington (3-9), which led 30-23 with under 6 minutes remaining.
Campbell threw to Fred Davis on a 8-yard scoring play, and 5 and 13 yards Devin Thomas for touchdowns.
The Redskins quarterback completed 30-of-42 passes and Thomas ended up with seven catches for 100 yards.