TEMPE, Ariz. — The Giants were trailing the Cardinals 20-0 at the half Sunday at State Farm Stadium and the road to recovery looked bleak, with the hole they’d dug themselves with the putrid first-half performance appearing as deep as it was dark.

Cliches be damned, the only way out for the Giants was one play at a time.

That’s the way Darren Waller saw it, because he knows one day at a time better than anyone inside the Giants locker room.

As a recovering alcoholic, who was also addicted to pain killers and cocaine, Waller saw not only his football career but, more importantly, his life rest on the precipice of peril as he lost his NFL playing privileges and spent more than a month in rehab in 2017.

So, the Giants’ 31-year-old tight end, who was acquired in a trade with the Raiders in the offseason, has a better understanding of patience than most.

That’s why Waller never felt panic in that Cardinals game despite how badly it was going for his team.

The Giants, of course, won the game, 31-28, overcoming a 28-7 third-quarter deficit, by making one play at a time.

Part of that process was Waller affecting the game for the first time as a Giant, catching a total of six passes for 76 yards, but five of those for 64 yards came during the second-half comeback, most in clutch, must-have moments.

“With my life journey, I’ve been knocked down on my ass not knowing what I was going to do and I couldn’t look too far into the future,’’ Waller told The Post. “I had to handle things like right where I was. The second half of that game reminded me of that.’’

Waller loved the resolve his teammates showed in the comeback against the Cardinals.

“As a guy that’s had the life journey that I’ve had, the qualities I respect in man the most is not when things are going great and you’re out running in the front and everybody’s dancing and having fun,’’ Waller said before the Giants travel to San Francisco to face the 2-0 49ers on Thursday night. “It’s when things get tough and you’re in that hole and you can start pointing fingers and getting angry and worrying about what you can get out of the game, and guys come together. That’s what I respect the most.

“Seeing that, that’s what really lights me up.’’

So, too, does patience, because that’s something that’s become a lifeline to his poignant journey.

“When I went to rehab and came out, it was probably 10 or 11 months until I got reinstated into the league and I was trying to figure out my life and trying to reform my character,’’ Waller recalled. “I had to be patient with myself in that process, because I wanted good things to happen and I wanted to get back to having a good life. And it took a while. I couldn’t rush those things.

“Then, when I got reinstated, I got cut by the Ravens and I was on the practice squad for 11 weeks in 2018 even though I felt like I was ready to play and contribute to an offense. But I had to wait even more. When things don’t go your way, I’ve been forced not to get so tense or disappointed or swayed one way of the other.’’

It’s human nature to want everything at once, and that’s an urge Waller learned to fight.

“It was all up here for me,’’ he said, pointing to his head.

Everyone knows the kind of dynamic, physical talent the 6-foot-6, 255-pound Waller brings. He caught 90 passes for 1,145 yards and three TDs in 2019 and 107 for 1,196 yards and nine touchdowns in 2020 for the Raiders.

What isn’t as obvious to the outside world — because there are no statistics for this — is the impact Waller has and will have inside the Giants’ locker room.

“He’s a leader, he’s been through a lot of different things, he’s seen a lot, he’s experienced a lot,’’ safety Xavier McKinney, who’s also a team captain, said.

“He’s extremely level-headed,’’ quarterback Daniel Jones said. “His demeanor is always the same. He’s consistent in that approach and has been in the league for a long time, so he’s seen a lot. He’s kind of a steady presence in the locker room that guys can look to as a leader.’’

When Giants head coach Brian Daboll was doing his research on Waller before the team traded for him, he couldn’t find anyone to say a negative thing about him.

“The people that I’ve talked to, they spoke glowingly of him in terms of being a professional, how important his craft is, what a good teammate he was, and the production of the player,’’ Daboll said.

Now it’s up to Daboll and offensive coordinator Mike Kafka to find every way possible to get the ball into Waller’s hands. His performance against the Cardinals Sunday was a mere taste of what the Giants hope is to come.

For his part, Waller will, of course, remain patient.

One play at a time. One game at a time.

One day at a time.