The Giants’ defense weighs itself on an imaginary scale that shifts with everything the team’s offense does or doesn’t accomplish. If the Giants score three points, then anything less than perfection by the defense is failure. If they can’t score any, well, there are turnovers and safeties and absolutely zero excuses.

So forget the fact that the Giants held the Cowboys to 19 points Sunday. The defense has been weighed, and according to coordinator Steve Spag nuolo, it was found wanting.

“That’s how we feel,” Spag nuolo said Friday, responding to the idea that his players la mented their inability to key in on a big turnover. “We had a mission today to make sure we got two [turnovers in practice] and I think we got it . . . The guys take a lot of pride in that. What was the final score? 19-3? We had to hold them to two points. That’s the bottom line. [They can] find a way to get a safety and [we] win the game — not let them score. I think we should all feel like that.”

It’s not what anyone expected and certainly not what anyone wanted, but after an off game by Eli Manning and the offensive line, the absence of Odell Beckham Jr. (ankle) and Brandon Marshall’s disappearing act Sunday, the Giants’ defense finds itself pushed to the forefront. Things won’t get much easier Monday night against the Lions, and the pressure is on.

“You don’t let it affect you, but you’ve got to have that pressure on yourself and on the unit,” cornerback Dominique Rodgers-Cromartie said. “We’re not sneaking up on anybody. Expectations should be to go out there and dominate. We have a chance to get off the field or to make those plays, I think we should make them.”

Spagnuolo highlighted his unit’s inability to contain the Cowboys on third down Sunday, including a third-and-12 opportunity. The run defense needed work, he said, and they need to make a better effort in containing “leaky yards” — keeping teams to two or three when they’re pushing for five or six.

“As defensive players and coaches, we don’t blame anybody but ourselves for too many plays,” he said. “We go look at it and say what could we have done to keep us in the game, make it a one-possession game, so maybe Eli gets the ball at the end of the game and who knows? Any time you keep it to a two-possession game, which we did until really all the way through — you can win a game in four plays.”

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Either way, you “find a way,” he said. “That was a good football team, a good offense we played. If I say I would have felt better if we held them to six or nine, we still would have lost. So we have to do better than that.”

Even if they have to do it all themselves.

Notes & quotes: Tackle Bobby Hart was limited at practice. Linebacker Keenan Robinson was in pads but still was in the concussion protocol.