The Chargers were licking their chops and no one could blame them.

Los Angeles, a team under new coach Jim Harbaugh that was built to run first, second and third, was playing the Arizona Cardinals, which boasts of a rush defense which deviates between dreadful and disgusting.

But a Monday night matchup which leaned in the Chargers’ favor ended up being a disaster in the desert. Instead of imposing their will and their vaunted run attack on the hapless Cardinals, the Chargers had their wings clipped.

The final score of 17-15 tells part of the story, with L.A. settling for five Cameron Dicker field goals in a game in which quarterback Justin Herbert threw for a season-high 349 yards and zero touchdowns.

When it became clear that the Chargers (3-3) were running in quicksand, they asked Herbert to do something that Harbaugh preached would no longer be a thing. They plopped the offense, and the game, on Herbert’s broad shoulders and gave him the OK to play hero ball.

It didn’t work, just like that Hail Mary of a scheme was seldom successful under the other NFL coaches Herbert played under, and were eventually shown the door: Brandon Staley and Anthony Lynn.

When Harbaugh burst into the Chargers lobby as everyone heralded his arrival, it was quickly clear how the former Michigan coach was going to construct his squad.

He let his proven pass-catchers flee (Keenan Allen and Mike Williams), he declined replacing them with a standout receiver with a first-round pick, going instead with a right tackle (Joe Alt) and he beefed-up the physicality of the backfield by signing free-agents JK Dobbins and Gus Edwards.

Add all that up and that should result in a victory against an Arizona defense which was purged for 179 rushing yards in the previous week by the Green Bay Packers.

Numbers like that make the Chargers’ coaches smile as if someone said, “cheese.” Instead, they left Arizona with the look of someone who just sniffed the pungent aroma of some moldy limburger.

Among the reasons Harbaugh was distraught during the game’s closing minutes, and after it, was that he felt two calls didn’t go the Chargers’ way. One one was on a pass interference, or holding, that wasn’t called and the other was on an unnecessary roughness call, that was.

What became clearer than those muddled decisions is that if the Chargers can’t run the ball, they are cooked.

In addition to shoving a handful of playmakers out during the offseason, their current pass-catching core is ailing with Quentin Johnston (ankle), Derius Davis (hamstring) and D.J. Chark Jr. (groin) idle in Arizona.

Herbert did his part, despite evading rushers nearly every time he found the pocket. That he threw for nearly 350 yards while completing 27 of 39 passes speaks highly of him and how poorly this roster was constructed and executed, if it can accumulate but 60 yards on the ground.

Two things stick out: Herbert was sensational regardless of the spotty pass protection and a running game which was somewhere other than in Arizona.

“It’s a razor-thin margin in this league,’’ Harbaugh said to reporters, seeking a silver lining that few saw. “We’re a couple of plays away from putting up a lot of points.”

Or plopping Herbert, who’s already saddled with a bad ankle, in the hospital unless his blockers start blocking and his runners start running.

“Kept waiting for the running game to pop,’’ said Harbaugh, who’s being paid $16 million annually to make it happen. “But we weren’t able to.’’

Any loss is bad in the NFL, but some reveal a team’s blemishes more than others. It was no secret that the Chargers were embracing the run this season and that the passing game would be a second option.

What’s troubling is that strategy wasn’t good enough against a soft target and one that could have fueled a midseason run.

Beat the Cardinals, and just maybe the Chargers find gold against their next three rivals in the New Orleans Saints, Cleveland Browns and Tennessee Titans and are in the playoff race.

Instead it was the Cardinals’ rushing game waltzing all over the Chargers to the tune of 181 yards. And their defense kept the Chargers out of the end zone.

No offense, but until the Chargers unearth a way to penetrate the goal line, this season could soon replicate last year’s 5-12 pileup.