The Cowboys can thank their defense, which has become one of the league’s more dominating units on that side of the football.

And, surprisingly, they can thank the roster-tinkering acumen of Jerry Jones, their owner and general manager who made the trade for wide receiver Amari Cooper that turned around their season.

Those factors have Dallas in prime position to win the NFC East.

The Cowboys all but wrapped up the division title Sunday evening when they outlasted the Philadelphia Eagles, 29-23, on a tipped-pass touchdown catch by Cooper in overtime. The play ended a thrilling game at AT&T Stadium and capped another fantastic performance by Cooper.

“This,” Tony Dungy said later on NBC, “is why they gave up a first-round draft choice to get him.”

Indeed it is. That first-round pick that Jones and the Cowboys sent to the Oakland Raiders to obtain Cooper was intensely debated at the time. Was it too much? Cooper had been a Pro Bowl selection in each of his first two seasons in Oakland, but he’d failed since then to maintain the same level of production. Had Jones’s tinkering on the football side of the operation led to the Cowboys overpaying?

No one is wondering that now, not with the Cowboys on a five-game winning streak. They have a 5-1 record since making the trade with Cooper becoming a difference-maker on offense. He had 10 catches for 217 yards and three touchdowns against the Eagles, topping his eight-catch, 180-yard, two-touchdown performance against the Washington Redskins on Thanksgiving.

“I’ve always believed the trade I made for Tony Dorsett was one of the greatest trades in NFL history,” former longtime Cowboys executive Gil Brandt wrote on Twitter. “At the risk of being too reactive the trade Jerry Jones made for Amari Cooper could end up being right up there. I loved it for Dallas when it happened, it looks even better now.”

The Cowboys, with a record of 8-5, have a two-game lead on the Eagles and Redskins in the NFC East. They hold the tiebreaker advantage over the Eagles by virtue of beating them twice. The Redskins look done, having succumbed to their injuries at quarterback and along their offensive line. The New York Giants, at 5-8, got started too late. The division race essentially ended with Cooper’s touchdown catch in overtime Sunday.

“It’s been a dream come true,” Cooper told Fox after the game. “When I was young and thought about playing in the NFL, this is the experience …. It’s exciting.”

The final touchdown was aided by some very good fortune. The pass by Cowboys quarterback Dak Prescott was deflected by Eagles cornerback Rasul Douglas, but the ball went directly to Cooper on the carom. He made the grab and strolled into the end zone.

“I just stayed with the ball,” Cooper said, “and thank God.”

Prescott threw for 455 yards and three touchdowns on a 42-for-54 passing day. But his mistakes also kept the Eagles in the game. Prescott threw two interceptions and lost a fumble.

The Cowboys crafted a 9-0 lead on a trio of field goals by kicker Brett Maher, including a 62-yarder right before halftime. The Dallas defense was bottling up the Philadelphia offense and controlling the game.

But Prescott made a terribly off-target throw that set up a touchdown for the Eagles, who missed the extra point. He lost a fumble to set up a tying field goal for the Eagles.

That Cowboys, on a pair of Prescott-to-Cooper touchdowns, seized a pair of seven-point leads in the fourth quarter. But the Eagles answered each time on touchdown passes by quarterback Carson Wentz, first to tight end Dallas Goedert and then to running back Darren Sproles. The Wentz-to-Sproles touchdown, with evened the game at 23, came after the Eagles were victimized by a dreadful offensive pass interference call against Goedert to nullify a long touchdown.

“In Dallas that’s … not offensive pass interference,” former NFL officiating czar Dean Blandino, now a rules analyst for Fox, wrote on Twitter.

No, it wasn’t. But the Eagles persevered and tied the game, with Coach Doug Pederson opting against a two-point conversion try that, if successful, would have given Philadelphia the lead in the final two minutes of regulation.

That seemed to go against Pederson’s daring nature. And the Eagles never got the ball again. The Cowboys’ drive toward a possible winning field goal at the end of regulation was undone by a bad snap and, later, a sack of Prescott. But the Cowboys got the ball first in overtime and went on an eight-minute drive which ended in Cooper’s third touchdown, converting a fourth-down along the way on a run by tailback Ezekiel Elliott.

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