Washington jumped into the last NFC wildcard spot with the result.
Seattle quarterback Russell Wilson masterminded a 96-yard touchdown drive in the game’s final three minutes and hit wide receiver Freddy Swain on a 32-yard touchdown toss, but was picked off by cornerback Fuller on the ensuing two-point conversion attempt.
Washington running back JD McKissic made his former team pay by catching a touchdown pass from signal-caller Taylor Heinicke and running for another score before being taken off in the fourth with a suspected head injury.
The Seahawks’ chances of making the playoffs appeared slim following the loss, which was their third in a row.
Washington, meanwhile, jumped into the last NFC wildcard spot with the victory and will next take on the Las Vegas Raiders in Nevada.