Washington quarterback Kirk Cousins drove the Redskins to a touchdown with 18 seconds left, bringing them within one point. But instead of kicking a score-tying extra point, Coach Mike Shanahan decided to go for the win with a 2-point conversion.
On the play, Cousins tossed a soft pass into the end zone, which was tipped away by Trufant, securing a victory for the Falcons (4-10).
Matt Ryan passed for 210 yards with an interception on 29-of-38 efficiency.
Steven Jackson supplied two TD runs for Atlanta.
Cousins, starting over the benched Robert Griffin III, passed for 381 yards with three touchdowns.
But he was also was picked off twice and lost a fumble for the Redskins (3-11), who committed seven turnovers overall en route to a sixth straight loss.