GLENDALE, Ariz. — Coaches everywhere would drain their bank accounts on the black market to buy a bottle of whatever magic happened Sunday in the Giants’ halftime locker room.

The worst offense in the NFL — held scoreless for the first 91:17 of the season — became unstoppable as it scored on all five of its second-half possessions and saved the Giants’ season from a shockingly early point of no return with a 31-28 victory over the hapless Cardinals at State Farm Stadium.

As the Giants emerged from halftime trailing 20-0, it was a question of whether they could get first downs, let alone score.

Forget about winning.

Whether head coach Brian Daboll read the riot act or used a softer touch, Saquon Barkley scored two touchdowns, Daniel Jones rushed for one and threw another to Isaiah Hodgins, and Graham Gano kicked the tie-breaking 34-yard field goal with 19 seconds remaining to complete the improbable comeback.

Jones threw for 321 yards, with Darren Waller’s six catches for 76 yards sparking the offense.