ARLINGTON, Texas — They say it’s a game of inches, but the Eagles were a country mile behind the Dallas Cowboys on Monday night.

They were completely outclassed on both sides of the ball in a 41-21 rout at AT&T Stadium, and if not for the few inches Dak Prescott was stopped short of the goal line, the Eagles would have lost by more.

But 41 points would suffice in illustrating how coach Nick Sirianni and his defensive coordinator, Jonathan Gannon, aren’t yet ready for prime time.

Can they eventually get there? Of course. Sirianni had a strong debut on offense. And Gannon’s unit surrendered only 23 points in the first two games. But the game plan Monday night didn’t take into account the versatility of the Cowboys offense, and the Eagles never once had control of the game.

“First of all, I want to give credit to Dallas,” Sirianni said. “Dak — to see him play and operate in person — he’s a heck of a football player. [Cowboys offensive coordinator] Kellen Moore’s a really good coordinator, and I think he did a really good job — and Dak — of taking what our defense was giving them.

“Our plan was to limit big plays.”

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That has pretty much been Gannon’s plan from the start of the season, and for the most part his soft zones had worked. But all it took was one drive for Prescott to exploit the dreaded inverted Cover 2 — that left the middle of the field vacated — when he hit CeeDee Lamb for a 44-yard pass to set up Dallas’ first touchdown.

The Eagles rebounded, even after Jalen Hurts tossed a drive-killing interception on the ensuing drive, when Javon Hargrave forced a strip sack that resulted in a Fletcher Cox touchdown. And they managed to keep Prescott out of the end zone on the goal-line sneak a series later to keep the score knotted, 7-7.

But the Cowboys had already established their dominance up front as they pounded running backs Ezekiel Elliott and Tony Pollard up the middle. They gained 8, 7, 6, 5 yards on one first down after the other.

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Dallas doubled Cox or Hargrave, or sometimes both, and took its chances against the defensive ends when they cut back through lanes or inside zone runs. It shouldn’t have come as a surprise with the Eagles’ best edge-setting end — Brandon Graham — out for the season.

“They were in second-and-4, second-and-3,” Cox said. “And that’s one thing we’ve been known for — stopping the run. Obviously, up front, I’ve got to take more control of that.”

Cox was garnering a lot of attention, and he was coming off an illness that forced him to miss most of practice last week. But the $100 million defensive tackle has to do better than zero tackles.

Cox wasn’t the only one at fault, and Graham is only one player. Josh Sweat, Derek Barnett, Ryan Kerrigan, and Milton Williams needed to contribute more than they did — nine total tackles and Sweat’s half-sack. Barnett needs to stop taking dumb penalties. And the Eagles’ linebackers needed to make more stops at the second level.

“It wasn’t that edge attack like we’ve had the last few weeks,” linebacker Alex Singleton said. “It was more downhill, so more on [the linebackers] than the edge guys.”

Gannon was also keeping his box relatively light with deep zones. Prescott was just taking what the Eagles were giving, and he either checked to runs, or he threw underneath. He completed 21 of 26 passes for 238 yards and three touchdowns.

Sirianni said the offensive game plan was to keep pace with the explosive Cowboys. So he schemed an attack that had Hurts throwing early on downs and from the pocket. There was a 38-yard completion to tight end Dallas Goedert on the first play, but the quarterback couldn’t sustain efficiency when he dropped deep.

Hurts looked skittish. And with two inexperienced offensive linemen at left tackle (Andre Dillard) and right guard (Landon Dickerson), it was easy to understand why. But where were the play-action roll-outs that set a new spot for the young quarterback? Where were motions at the snap to divert attention?

The failure of Gannon’s defense was also on Sirianni’s offense. Of course, the opposite could be said, as well.

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“It’s on us,” Cox said. “We got to get off the field.”

Elliott and Pollard had 116 yards on 21 carries (5.5 average) by the break. Dallas ran 42 plays to the Eagles’ 18 in the first 30 minutes. Defenders were gassed. Hargrave, who continued his high level of play with two sacks, tapped out at one point. Cox left briefly with cramps.

And the Eagles’ depth on the D-line, which was supposed to be a strength, was exploited when rookies Tarron Jackson and Marlon Tuipulotu were forced to take snaps. Sweat just signed a $40 million contract extension, but Williams started over him.

Gannon likely wanted more size on the edge. He’s been pushing the left end inside in 3-4 looks, and Sweat is 25 pounds lighter than Williams. But so is Kerrigan, and he’s been playing out of position for all three games so far.

It didn’t cost Gannon in the first two, but the Cowboys took advantage of those mismatches inside. And when they were productive on early downs, Prescott had short second and third downs and had the Eagles’ linebackers and safeties off-balance.

He hit tight end Dalton Schultz for a 19-yard first-quarter touchdown when he got over Singleton and the secondary. And he hit him in the fourth to cap the scoring on a 22-yard screen pass. In between, he converted a fourth down at the 2-yard line when he found receiver Cedrick Wilson in the back of the end zone.

Prescott had all day because Gannon rushed only three and dropped eight in coverage. The execution wasn’t great. Cornerback Darius Slay lost Wilson. But how long can the coverage be expected to hold?

Gannon isn’t suddenly a dunce. He’s a first-time coordinator working for a first-time head coach. Those aren’t excuses. It’s just reality. But they need to do better than they did in their third game if the Eagles are to build toward a brighter future.

“It’s Week 3. We got a long season to go,” Singleton said. “If we’re going to hang on this, it’ll kill us. But if we move on, get ready, and Kansas City’s coming to town. No one’s feeling sorry for us. So it’s time to buckle down and go play football.”

Patrick Mahomes and the Chiefs are coming to town in five days. Hang on, it could be a bumpy ride.