ARLINGTON, Texas — The Dallas Cowboys may have lost more than just a football game Monday night when the Washington Redskins beat them 20-17 in overtime at AT&T Stadium.

Quarterback Tony Romo left in the third quarter with what appeared to be an injury to his surgically repaired back, though he returned in the fourth quarter.

As for the Redskins (3-5), they might have found new life. Washington quarterback Colt McCoy, a third-stringer coming into the season, started for the first time in nearly three years and engineered the upset.

McCoy did more than just keep the seat warm as the Redskins await the return of starter Robert Griffin III. McCoy passed for 299 yards, and his 16-yard pass to tight end Jordan Reed set up the game-winning field goal in overtime.

McCoy (25 of 30, one interception) was rolling to his left when he deftly dropped a floater into Reed’s hands down the sideline. Kicker Kai Forbath drilled a 40-yarder four plays later.

Running back Alfred Morris rushed for 73 yards and a touchdown as Washington won for the first time on the road this season in four tries. Wide receiver DeSean Jackson caught six passes for 136 yards.

Cowboys backup quarterback Brandon Weeden led two scoring drives in Romo’s absence. Romo completed one of three passes for a loss of 1 yard in overtime, and his incompletion on fourth-and-3 ended the game.

Dallas (6-2) saw its six-game winning streak end. The NFC East leaders were looking for the franchise’s first 7-1 start since 2007.

Romo was hurt while being sacked by linebacker Keenan Robinson. Romo remained on the field for several minutes while being attended to by the Cowboys’ medical staff. He eventually walked gingerly to the sideline accompanied by coach Jason Garrett.

Cowboys running back DeMarco Murray extended his NFL record with his eighth consecutive 100-yard rushing game to open the season. The NFL’s rushing leader ran for 141 yards on 19 carries, putting him over 1,000 yards on the season. He also lost a fumble in the first half.

Romo finished 17 of 28 for 209 yards and a touchdown. Weeden completed four of six passes for 69 yards and a score. Murray led the Cowboys with 80 receiving yards on four catches.

On the first possession after Romo was hurt, Murray broke off a 51-yard run on Weeden’s first play. The run set up kicker Dan Bailey’s short field goal to tie it 10-10.

McCoy answered with his best series of the night to put the visitors ahead 17-10. A 45-yard pass to Jackson set Washington up at the Dallas 8. McCoy ran the final 7 yards on a third down less than two minutes into the fourth quarter.

Weeden responded by engineering a long touchdown drive that included a 23-yard screen to Murray and ended with a 25-yard pass to tight end Jason Witten with 9:27 play.

Morris put the Redskins back on top in the third with his 5-yard touchdown run. Washington took the opening kickoff of the second half 80 yards in eight plays to lead 10-7.

Dallas took a 7-3 lead into locker room despite an inconsistent first half. The Cowboys punted or turned the ball over on each of their first four drives.

Wide receiver Dez Bryant’s 5-yard touchdown catch with 4:45 remaining until halftime finally put the Cowboys on the board. Romo’s pass out in the flat was one-handed by Bryant just inches off turf before the receiver stretched the ball over the goal line.

The Redskins went up 3-0 early in the first quarter on Forbath’s 44-yard field goal. A 37-yard punt return by Andre Roberts set up the score.

Washington blew a golden chance to add to its lead after recovering a fumble on the Dallas 25-yard line. Two plays later, McCoy threw into double coverage in the end zone and was picked off by safety J.J. Wilcox.

The Cowboys gave the ball back again after Murray was inside the Washington 10. Fighting for extra yards after nearly taking a screen pass the distance, the NFL’s leading rusher fumbled the ball for the fifth time this season.

Dallas had a 218-127 edge in total offense at the break. Romo had 172 yards passing to McCoy’s 112. Murray accounted for 120 total yards before the break.

NOTES: Washington QB Colt McCoy made his first start since Week 14 of 2011, when he was playing for the Cleveland Browns. … The Redskins and Cowboys met on “Monday Night Football” for the 16th time, second to Raiders-Broncos (17). … Dallas RB DeMarco Murray and Hall of Famer Emmitt Smith are the only players in franchise history with at least 900 yards rushing in any seven-game span. Murray came into Monday with a league-high 913 yards. Murray has a 1,000-plus-yard season for the second time in his career. … Cowboys LB Bruce Carter returned after missing three games with a quadriceps injury. Dallas’ inactives: QB Dustin Vaughan, OT Doug Free, OT Donald Hawkins, DE Jack Crawford, DT Davon Coleman, LB Keith Smith and S Jakar Hamilton. … Redskins QB Robert Griffin III (ankle) was inactive, but he did take part some pregame drills. Other Washington inactives: OT Tyler Polumbus, WR Aldrick Robinson, CB Greg Ducre, OG Spencer Long, DE Clifton Geathers and LB Jackson Jeffcoat.