ASHBURN, Va. — Colt McCoy did something on Monday night that no Washington Redskins quarterback had done in 51 weeks: play an entire game and win. And not just any game. The erstwhile third-stringer led Washington to a 20-17 overtime triumph over archrival Dallas, its first NFC East victory since the conquest of the Cowboys in the 2012 win-or-go-home finale that clinched the Redskins’ only division title of the millennium.

In his first start in almost three years, McCoy completed 25 of 30 passes for 299 yards and ran for a touchdown while playing his best in key situations unlike Kirk Cousins, whom he relieved at halftime the preceding Sunday against Tennessee.

After Dallas tied the game 10-10 with 4:03 left in the third quarter, McCoy connected on 14 of his ensuing 15 attempts for 162 yards. The former University of Texas star hit all five of his passes on the game-winning drive back in his native Lone Star State as the Redskins improved to 3-5 with their second straight victory, upsetting the previously 6-1 Cowboys.

“I just tried to stay composed,” said McCoy, who threw an interception two plays after the heavy underdog Redskins — already leading 3-0 — had recovered a fumble at the Dallas 25 late on the first quarter. “I don’t know if it was nerves. I was just a little bit rusty. I missed a few things. I called a play wrong in the huddle one time. Just all the little things that come up when you haven’t played in a while. … It’s been a tough road, but I’ve learned a lot from experience. I’m thankful that my teammates hung with me and stuck with me. (But) we started converting on third downs and found a way to stay on the field, and that (was) huge against a (team that was) leading our division. We found a way to win.”

Of course, first-year head coach Jay Gruden was impressed with McCoy, who found receiver DeSean Jackson for completions of 45 and 49 yards, connected with fullback Darrel Young for 12 yards on a critical fourth-and-1 and with tight end Jordan Reed on a pair of clutch third down throws.

“(Colt) wasn’t perfect by any stretch but he competed his butt off, made some huge throws, some good scrambles, a great (7-yard) quarterback draw for a touchdown,” Gruden said. “It was blocked pretty good but to find that crease and dive in the end zone is pretty gutsy. You love to have that competitive spirit at your quarterback position. You never really quite know until you see him out there with the lights on and under pressure, so I just love his competitive spirit and the way he handled the pressure.”

McCoy played so well that he also relieved the pressure on Gruden to turn to Robert Griffin III this Sunday at Minnesota just seven weeks after the regular starter dislocated his left ankle.

“We’re not going to rush Robert back,” said Gruden, whose team has its bye after visiting Minnesota, which means that Griffin likely won’t return until the Nov. 16 game against Tampa Bay. “Until we feel like he’s 100 percent, Colt will play. And Colt did a great job obviously leading us to victory against Dallas. It’s all going to be predicated on when the doctors say (Robert’s) 100 percent, when Robert feels like he’s 100 percent and when I feel like he’s ready to take the game time reps.”

That’s fine with Pro Bowl offensive tackle Trent Williams, who said, “Colt did a great job. He did everything we asked him to do. It’s not like he’s a rookie being thrown into the fire. He’s well-seasoned. He knows how to run this offense. We have all the confidence in the world in Colt.”

As for beating the Cowboys, Gruden allowed himself a little bit of crowing after a rough start to being in command for the first time.

“The entire country thought there was no shot the Redskins could hang with the Cowboys,” he said. “The whole country except the 53 guys in here and the coaches. We expected to win and we came out and played like it. That’s a great football team we beat. (NFL rushing leader) DeMarco Murray’s a monster and (they have) a good defense. We’ve got to have fun with this victory. Winning at Dallas is always important … (the) rivalry, (a) division game, but we’re 3-5, so we have to continue to compete and work very hard to get ready for Minnesota.”

Defensive end Jason Hatcher, a Cowboy from 2005-13, exulted when he called heads and won the overtime coin toss and when the Redskins won, but normally mild-mannered outside linebacker Ryan Kerrigan might have enjoyed the upset the most.

“We heard a lot of crap being talked about us this week,” Kerrigan said. “(People saying that) we had no chance. We (saw) the guys on CBS just laughing, saying, ‘Awww, the Redskins have no chance.’ I guess we’re laughing now.”

REPORT CARD VS. COWBOYS

PASSING OFFENSE: B+ — Colt McCoy didn’t throw for 300 yards or even for a touchdown in his first start in almost three years, but the usual third-stringer still sparkled in completing 25 of 30 passes for 299 yards. As expected, McCoy’s two long completions both went to big-play receiver DeSean Jackson, who had six catches for 136 yards.

After a quiet start, tight end Jordan Reed finished with a team-high seven catches. Receiver Pierre Garcon and backup tight end Niles Paul each had grabs of at least 20 yards and fullback Darrel Young rumbled 12 yards with a reception on fourth-and-1. McCoy was sacked three times and hurried on three of his other 30 dropbacks, but the protection was pretty solid although right guard Chris Chester was a liability on a couple of occasions.

RUSHING OFFENSE: B — Looking their dreary selves of the past month on the ground at halftime, Alfred Morris and Co. finally got it going after that, rushing for 100 yards on 21 carries the rest of the way with the Pro Bowl back producing 62 of those yards and a touchdown on 13 runs. Backup Roy Helu gained 29 yards on five attempts while McCoy scored on a 7-yard draw. Rookie Silas Redd surfaced with a five-yard run. The blocking got better as the game went on with Tom Compton making his first start at right tackle in place of the demoted Tyler Polumbus.

PASS DEFENSE: B — Dallas quarterbacks Tony Romo and Brandon Weeden compiled a 107.2 passer rating, but Washington won this battle. Cornerback Bashaud Breeland outfoxed Dex Bryant most of the night although the Cowboys’ star receiver did bull over the rookie and safety Ryan Clark on a 20-yard touchdown. Dallas tight end Jason Witten was left alone on a 25-yard score, one of his five catches for 70 yards. Receiver Terrance Williams had six catches for 69 yards and DeMarco Murray produced 80 yards on his four grabs as no one seemed to be able to cover the running back.

However, safety Brandon Meriweather had a huge game with seven solo tackles, two sacks and forced Romo to fumble. Keenan Robinson knocked Romo out for a while on another sack while fellow inside linebacker Perry Riley returned from two games on the shelf with his own sack. And outside linebacker Ryan Kerrigan added another to raise his team-high total to 7.5. Second-year cornerback David Amerson joined Breeland in performing well against Romo et al.

RUSH DEFENSE: D — The Redskins simply couldn’t tackle Murray, who ran 18 times for 90 yards, not counting a 51-yard gallop. Backup Joseph Randle added 23 yards on three carries. However, each back also lost a fumble as Breeland and Meriweather each knocked a ball loose. That was about the extent of the good news for Washington in this department. Robinson led the tacklers with 10, but too many of his stops and everyone else’s, were too far downfield.

SPECIAL TEAMS: B+ — Kicker Kai Forbath kicked a game-winner for the second straight week with the 40-yarder following a 44-yarder that opened the scoring. Forbath improved to 13 of 14 on the season and added three touchbacks among his five kickoffs. The coverage unit limited the dangerous Dwayne Harris to a 22.5 average on the other two. Harris did return one punt for 18 yards, but Akeem Davis, just promoted from the practice squad, slammed him for no gain on the other Tress Way boot that he tried to return. Way

continued his fine season by pinning Dallas on its 3-yard line for its final series of regulation on a punt that was downed by Trenton Robinson. Andre Roberts’ 37-yard punt return was his best special teams play in six weeks but he managed just two yards on his other one.

COACHING: A- — Not only did first-year coach Jay Gruden lead a 2-5 team with a third-string quarterback to an overtime victory against a 6-1 division rival, he and offensive coordinator Sean McVay teamed to call an excellent game that played to Colt McCoy’s strengths while also sticking with the running game despite a poor first half. Defensive coordinator Jim Haslett continually frustrated Romo and the Dallas blockers with blitzes that produced five sacks and a fumble, helping to make up for the absence of Orakpo and top cornerback DeAngelo Hall, who are both done for the year. Special teams coach ben Kotwica’s units are on the upswing.