Cam Sims (right) of the Washington Football Team catches a pass against Cameron Sutton of the Pittsburgh Steelers on Monday in Pittsburgh, Pennsylvania. Photo: AFP

Alex Smith threw for 296 yards and a touchdown on Monday, and the Washington Football Team stunned previously unbeaten Pittsburgh 23-17, preventing the Steelers from clinching an NFL playoff berth.

Washington's Dustin Hopkins kicked a 45-yard field goal with 2:07 to play and - after Jon Bostic intercepted a deflected Ben Roethlisberger pass - added another 45-yard field goal with 17 seconds remaining to seal the shocking victory.

Rallying from a 14-point deficit, the team that dropped its nickname this year over Native American racism issues improved to 5-7, winning its third consecutive game to match the New York Giants for the NFC East division lead.

The only Super Bowl champion with an unbeaten season remains the Miami Dolphins in the 1972 campaign.

The Steelers fell level with reigning Super Bowl champion Kansas City at 11-1 in a fight for the top seed in the American Conference and a first-round playoff bye.

Roethlisberger threw second-quarter touchdown passes of three yards to Diontae Johnson and 50 yards to James Washington as the Steelers took a 14-0 lead.

But Hopkins kicked a 49-yard field goal just before halftime, and Washington marched 82 yards in 14 plays over 6:44 to open the second half, a one-yard touchdown run by Peyton Barber pulling the visitors within 14-10.

Pittsburgh responded with Matthew Wright's first NFL field goal on the opening play of the fourth quarter.

But Smith flipped a 15-yard touchdown pass to Logan Thomas with 9:09 to play, lifting Washington level at 17-17.

Pittsburgh turned over the ball on downs at the Washington 28-yard line, and a one-handed catch by Cam Sims on a 29-yard Smith pass sparked the drive for the Hopkins go-ahead kick.

Thomas had a career-high nine catches for 98 yards, and teammate J.D. McKissic made a career-best 10 grabs for 70 yards.