Early in the fourth quarter, the Chargers faced third-and-9 at the 50-yard line. The Eagles defense had done its job on first and second down and on the money down, quarterback Justin Herbert would likely drop to throw.

Jonathan Gannon may have expected his four defensive linemen to get home with their ears pinned back. But Herbert had already torched the Eagles through the air. He had completed 23 of 24 passes to nine different receivers at one point.

Almost nothing Gannon had done was working. He blitzed a few times. He mixed up his rushes with five men on the line. But the Chargers were almost always a step ahead. And on this drop, Herbert had more than four seconds with the Eagles’ front four easily blocked.

He waited for a receiver to break open and hit Keenan Allen over the middle for 18 yards. Los Angeles would score a touchdown six plays later to take a 24-17 lead, and while the Eagles would respond to knot the score, that moment was emblematic of how Gannon’s defense performed in an eventual 27-24 loss on Sunday.

» READ MORE: Eagles-Chargers instant analysis: Close game, but the defense falters in the end, as L.A. wins it on a field goal

Herbert, overall, completed 32 of 38 passes for 356 yards and two touchdowns. His 84.2 completion percentage, amazingly, wasn’t the highest the Eagles have allowed this season. That honor went to the Raiders’ Derek Carr two weeks ago when he connected on 91.2 percent of his attempts.

But it’s been a recurring nightmare for Gannon and his pass defense this season. His unit has allowed five quarterbacks to complete more than 80 percent of their throws. Elite throwers such as Dak Prescott, Patrick Mahomes, Tom Brady, Carr, and Herbert have been responsible for those outings.

The Eagles, though, have made their jobs far too easy.

“Anytime you play a quarterback like Justin Herbert … you got to be on your ‘A’ game, and it starts with us as coaches,” Eagles coach Nick Sirianni said. “And I’m not going to say Jonathan anything because my name’s on that.”

Gannon doesn’t talk immediately after games, but it’s likely he’d fall on the sword for the performance. The first-time defensive coordinator has tried to mix up his coverages and rushes the last few weeks. He has had his secondary challenge more.

But his pre-snap disguise was mostly decipherable on Sunday. And when he went soft with his zones, Herbert knew where to attack. And Gannon just isn’t yet seasoned enough to compensate for what he lacks in personnel.

It wasn’t just the linebackers who struggled this time, however. Cornerbacks Darius Slay, Steven Nelson, and Avonte Maddox had collectively their worst game of the season. The Chargers used an assortment of personnel and tactics to hit the Eagles underneath.

The tight ends caught a combined 11 of 11 targets for 126 yards. Allen kept beating the corners on slants and quick outs and caught 12 of 13 for 104 yards. And receiver Mike Williams, while mostly kept in check deep, did hit a big one when Herbert dropped a 49-yard bomb in his lap midway through the third quarter.

Slay had tight coverage. But he would miss an open field tackle on tight end Donald Parham on an 8-yard catch-and-run touchdown a few plays, and leave later with a hamstring injury.

“It’s a really good football team with a lot of good weapons on it, so you have to account for a lot of people,” Eagles linebacker T.J. Edwards said. “I thought we had a great scheme coming in. Great execution for the most part. Just those couple plays when we needed them.”

Gannon’s defense broke only a few times in the first half. Slay had a fourth-down stop on the Chargers’ opening drive that went from 1-yard line to the other without a point. And there was a fourth-down run stop in the second quarter.

But the Eagles never forced L.A. to punt the entire game, the second time they achieved that dubious honor — the Chiefs in Week 4 was the first — this season.

Sirianni’s balanced offense did its best to keep Herbert off the field. And when quarterback Jalen Hurts tied the score, 24-24, with a 28-yard touchdown pass to receiver DeVonta Smith with just over six minutes left, the Eagles just needed one stop.

But the Chargers bled them and the clock on a 15-play drive to set up the game-winning field field. They converted two short fourth downs along the way, the second a Herbert sneak on the Eagles 28 with 1:45 seconds left.

The Eagles had a chance to force a relatively long field goal. But running back Austin Ekeler broke through the middle for a 16-yard dash, which set up the 29-yard game-winning field goal.

“Obviously, you want to get the stop,” Sirianni said. “I thought they did a good job of not jumping offsides. I thought they might kick the field goal … but they didn’t. And hats off to them.”

It had to be a helpless feeling for Sirianni and Hurts. But mostly for Gannon, who just hasn’t found a winning formula. He has tightened a few things up, going with Edwards and Davion Taylor at linebacker.

But the defensive line was built to be a strength and it has yet to record a sack at home. Herbert wasn’t hit once by a lineman.

“It’s definitely frustrating,” defensive tackle Javon Hargrave said. “We got great rushes, but you don’t really get a chance to show it when he’s getting the ball out like that.”

Herbert does have a quick release, but it’s not as if other defenses hadn’t forced him into mistakes. The second-year quarterback’s passer rating was below 70 in each of his two previous games. He’s still relatively inexperienced.

A full review of the game will spell out how often and effectively Gannon blitzed. At one point it seemed as if he should have emptied the tank just to do something different. Heck, if the Chargers scored on a zero blitz, at least it would have given Hurts and the offense a chance to come back.

“I thought when it was the right time, we sent pressure and we had looks that we had to get out of pressure because it’s not the right look to run those blitzes,” Edwards said. “Again, I thought schematically, we were ready to go, we were prepared, we had a great week of practice.”

But it was more of the same against top-tier quarterbacks. If there’s a silver lining — if it can be labeled that — the Eagles won’t face a quarterback as good over the next seven games. The Broncos, Saints, Jets, and two games each against the Giants and Washington await Gannon.

He has shown that he can scheme up a winning defense against lesser weights like the Falcons, 49ers, Panthers, and Lions. It may be enough to entrust him a future here. But you can learn on the job for only so long.