TEMPE, Ariz. — Honesty will be the best policy for the Giants as they unpack what occurred in their 31-28 comeback victory over the Cardinals Sunday and prepare for their Thursday night game at the 49ers, who’ll significantly raise the degree of difficulty.

The Giants need to be honest with themselves, with a full and deep understanding that Sunday’s performance at State Farm Stadium against an inferior Arizona team will not be good enough against the 49ers, a team with legitimate Super Bowl aspirations.

The Giants need to understand that they got away with one against the Cardinals and a repeat performance isn’t likely to bring the same result against the 49ers.

“We’re happy we got the win, but we’ve got a lot of things we have to f–king clean up,’’ safety and team captain Xavier McKinney told The Post inside the visitor’s locker room in the immediate aftermath of the game.

A day later, McKinney’s sentiment remained the same, minus the expletive.

“We can’t afford to do that against any team,’’ McKinney said Monday from the team hotel. “We can’t keep having slow starts as a team. We’ve got to correct it. There’s only so much talking we can do; we’ve got to go out there and execute the things that we practice and go over in these meetings. We definitely cannot keep doing that.’’

Quarterback Daniel Jones, who was a catalyst to the Giants’ 21-point second-half comeback, on Monday was still lamenting the poor first-half execution.

“There were some plays in the first half that we didn’t convert, and we’ve got to clean those up,’’ Jones said. “We can’t afford to start slow like that and miss opportunities early in the game to convert. That’ll be an emphasis of ours going forward.

“But we did show the fight and the resolve down the stretch and we made a lot of those plays and found a way to win,’’ Jones went on. “So, definitely proud of that and how the team responded. But there’s a lot to clean up certainly.’’

Offensively, the Giants will have to clean it up without star workhorse running back Saquon Barkley, who suffered a sprained ankle and is expected to miss about three games.

“Wink [Martindale, the defensive coordinator] will always say he’s our best defensive player, because when he’s on the field running the ball we’re on the sideline,’’ linebacker Bobby Okereke said. “Saquon is an incredible leader. This team is going to miss him, but we have a next-man-up mentality.’’

While Barkley is definitely out for the 49ers game, the status of starting left tackle Andrew Thomas, who sat out Sunday’s game with a hamstring injury, is in question.

That puts even more of an onus on the defense to start fast.

That, however, would mean creating some turnovers and producing some sacks — something the Giants have failed to do at all in the first two games. That’s a concern — particularly when two of their highest-paid players are defensive linemen Dexter Lawrence and Leonard Williams, neither of whom has made a significant impact so far.

Edge-rusher Kayvon Thibodeaux, the team’s top 2022 draft pick who promised to improve on his modest rookie season, has been almost invisible in the first two games. The next impact play Thibodeaux makes will be his first of the season. He has one solo tackle, one quarterback hit and no sacks through the first two games.

Asked why the team has no sacks or turnovers, McKinney put on an optimistic front.

“We’ll get there,’’ he said. “It’s not where we want things to be right now, but we’re fighting though adversity and we’ve just got to keep pushing and keep doing our jobs and know as long as we keep doing the things we’re doing, it’ll come. We’ve just got to be patient and not try to go out the framework of our defense and what Wink calls. Stick to the plan and we know they’ll come in bunches.’’

Okereke also offered optimism.

“Yeah, we’ve got to start fast and create turnovers,’’ he said. “That’ll be the key to this game. That’s a recurring theme in the first game and the second game. But I think we’re building off the momentum of the second half [against the Cardinals] and responding to adversity. We’re going to need to lean on the lessons we’ve learned through this adversity.

“Execution fuels energy. When we’re executing and making big plays, we’re celebrating and hyped-up and feel like we can’t be stopped.’’

That would be a nice change for a team that’s spent far too much time stopping itself — on both sides of the ball — in the first two games.

That’s the honest truth.