GLENDALE, Ariz. — For too much of Sunday afternoon in Arizona, it looked like Dallas 40, Giants 0 last Sunday night was no aberration after all.

It looked like the damn, sobering truth.

The Giants fell behind the Cardinals 20-0 at halftime and trailed 28-7 midway through the third quarter at State Farm Stadium and the hole looked like it was getting deeper and darker.

Not just for this game. For this season.

The saddest part was that it looked like there was nothing to embrace about this Giants team, a year after there was so much to celebrate and embrace about last season’s upstart group that went to the playoffs when few expected it to make that kind of jump so quickly.

The most detestable element to last week’s loss to the Cowboys — at home and in the season opener — was the glass chin the Giants showed in that game. The Cowboys punched them in the mouth early and the Giants had no response, showing no fight and no anger.

This is exactly where this game Sunday in Arizona was headed — against a far inferior team to Dallas, and that made it even more unacceptable.

And then everything changed.

The Giants finally gave their fans something to embrace and, of all ironies, it was the very thing that was missing in the opener: they showed some stones. They showed resilience. They showed that they can get angry, fed up and do something about it.

Suddenly, a team that looked like it was playing with no urgency and — worse — no heart, was playing like it was trying to save its season.

The Giants rallied from an abyss that felt equal parts disgusting and hopeless and overcame the Cardinals 31-28.

The improbable and stirring victory sends them to San Francisco for their Thursday night game against the Super Bowl-contender 49ers not with their season spiraling, but with hope and belief in each other.

“We talked before the game about adversity and we talked about if we got into another situation like last week when we were facing adversity that we’re going to dig ourselves out,’’ receiver Sterling Shepard told The Post. “You’ve two ways to go when you’re back is against the wall: you can sit there and just take it or you can fight your way out. So, we made a pact together in the locker room at halftime, and that’s what we did.’’

The Giants weren’t just losing to the Cardinals, they were being outclassed, outworked and out-executed by a team considered to be one of the worst in the league. A team with a quarterback — Joshua Dobbs — playing on his sixth NFL team in seven seasons, having started only nine games before Sunday.

Shepard revealed the theme of head coach Brian Daboll’s message inside the locker room at halftime: “Our backs are against the wall. Are we going to fight or what?’’

“So, that’s what we did,’’ Shepard said.

“We came together at halftime and we just had a sense of urgency,’’ said receiver Isaiah Hodgins, whose 11-yard TD catch tied the game at 28-28 with 4:25 remaining. “We rallied together. We got together and talked about all the time in the offseason we spent with each other and the camaraderie we built. You find out about that now. You don’t find out how close you are when you’re up 30-0, you find out when you’re down.’’

Quarterback Daniel Jones, who was a primary engineer in the comeback, completing 26 of 37 passes for 321 yards, two TDs and one INT, used the words “fiery’’ and “passionate’’ to describe Daboll at halftime.

Safety Xavier McKinney said Daboll’s message at the half was: “Don’t talk about it, be about it.’’

“You saw a a little bit of a lot of emotions,’’ said tight end Darren Waller, who caught six passes for 76 yards and was a big factor in the comeback. “You saw frustration, you saw disappointment, you saw some anger. And at the end of that it was like, ‘All right, what are we going to do about it?’ ’’

The play that ignited the turnaround was a 58-yard pass from Jones to rookie receiver Jalin Hyatt on the first play from scrimmage in the second half — Haytt’s first NFL reception. Two plays later, Jones ran it into the end zone from 14 yards out for the Giants’ first points of the season, cutting the Arizona lead to 20-7.

Jones, who usually shows about as much emotion as an accountant or an actuary, went nuts after he scored, looking like he might give Waller a concussion with a celebratory head butt.

“He head-butted the crap out of me,’’ Waller said. “But that’s the stuff you love.’’

To that point in two games this season, the Giants hadn’t had a single moment to celebrate.

Now they go to San Francisco a different team at 1-1, not one staring at the impending doom of 0-3.

“No game is ever over,’’ linebacker Bobby Okereke said.

Not Sunday’s game.

And now, not the season.