PHILADELPHIA — One mindless play changed everything for the Giants Monday night.

One mindless play injected life into the previously lifeless Eagles.

One mindless play led to the worst Giants loss of the season to date — yes, even worse than the blown fourth-quarter leads in Dallas and against the Falcons in the opening two weeks.

You cannot blame the Giants 27-7 loss to the Eagles Monday night at Lincoln Financial Field entirely on third-year defensive end Damontre Moore. There were plenty of culprits who helped author this mess of ugly football for the Giants, who looked like pretenders residing in sole possession of first place in the NFC East entering the night.

But you can trace the Eagles’ resurgence on this night directly back to Moore’s completely unnecessary roughing the passer penalty in the first quarter, because it woke the Eagles up, ticked them off perhaps, gave them life.

“It was a very, very bad penalty,’’ coach Tom Coughlin said. “I didn’t notice any surge [of energy from the Eagles], but it was a bad penalty. You can’t play like that. That’s bad football.’’

The Giants had a 7-0 lead and Eagles had just gotten the ball back on an interception by their linebacker, DeMeco Ryans. The Eagles were facing a third-and-10 from their own 22-yard line and their quarterback, Sam Bradford, under pressure, dumped a short pass off to Darren Sproles for a 3-yard gain.

But, instead of having to punt, the Eagles got a free first down because Moore unnecessarily drove him into the turf — giving him the business — and was called for the 15-yard penalty that changed everything.

First down Eagles, who were a dead team walking at the time. Suddenly, the Moore penalty injected life into them. And four plays after the penalty, Bradford connected with receiver Riley Cooper on a 32-yard touchdown pass.

Now the game was tied at 7-7 and the restless sellout crowd at the Linc was rocking.

“There’s no excuse,’’ Moore said. “I’ve got to get my football IQ and awareness up and get a better understanding of the rules so I can eliminate these penalties. I take full responsibility for it. It’s a learning mistake and I’ve got to fix it. I’ve got to eliminate the mistakes.

“Honestly, I think it was just part of me having poor football IQ, not aware of the rules of dumping him, because I dumped him. I was just trying to make a play and be a high-energy guy. I’m going out there and I’m trying to run from sideline to sideline and hit someone as hard as I can.’’

When Moore reached the Giants sideline coaches and players immediately got after him about the rule.

“That was the penalty — me driving him into the ground,’’ Moore said. “The refs didn’t say anything to me, but the coaches told me and other players told me that you can’t do that.’’

The Eagles would score the next 20 points after tying the game while the Giants, who looked so in control in the opening minutes of the game, looked more dysfunctional with each minute that passed.

It was all so disillusioning for the Giants, who entered the game at 3-2, riding a three-game winning streak and had a chance to separate themselves from the 2-3 Eagles.

Now, the Giants and Eagles are tied at the “top’’ of the NFC East at 3-3, yet it hardly feels like the Giants have a piece of first place at all.

Blame it on Damontre Moore.