After the Chargers beat the Las Vegas Raiders on Sunday, Los Angeles coach Jim Harbaugh told his players that the biggest improvement during the season comes between Weeks 1 and 2.

It’s part of the Harbaugh philosophy, probably handed down from their father, Jack, a former college coach himself, to his sons, Jim and John.

It’s true, which is why first-year defensive coordinator Zach Orr is forgiven for the team’s lackluster performance in the Ravens’ 27-20 loss to the Kansas City Chiefs on Thursday.

The performance was on par, especially against a lethal, fast-paced offense like Kansas City’s. But it can’t happen again Sunday at home versus the Raiders.

“I’ve been saying that for 17 years here,” John Harbaugh said with a laugh during a light moment with the media on Monday.

But the performance against the Chiefs was no laughing matter. It’s different here in Baltimore because the Ravens and defense are synonymous. It’s the franchise of Ray Lewis, Ed Reed and Terrell Suggs.

The Ravens looked lost Thursday night. Not only did they give up 353 yards in total offense, but their best players — middle linebacker Roquan Smith and All-Pro safety Kyle Hamilton — missed tackles. Baltimore also had to use two timeouts within the first five minutes of the third quarter. They could’ve used those when quarterback Lamar Jackson was driving the Ravens down the field on the final drive.

The Ravens talked about communication issues after the game, but Harbaugh emphasized the Chiefs’ substitution packages more.

“That’s something that was really not so much a communication issue, just a volume issue probably as much as anything,” he said. “We’re looking at that really hard [with it being] the first game of the season in that kind of environment. The other issues were more just the way we played the plays. Maybe communication was used [by our players] in kind of a general term.

“The substitution issues were legit, certainly. [We] probably had too many substitution groups up, to be honest. We were trying to play a lot of different guys and get them in there, situationally, against a no-huddle team. … “We didn’t do a great job.”

Honestly, it was to be expected. The Ravens lost three defensive coaches from a year ago — defensive coordinator Mike Macdonald, defensive line coach Anthony Weaver and secondary coach Dennard Wilson — so there was always going to be some mayhem shuffling players in their first real game action, especially against Kansas City’s up-tempo offense.

Plus, unlike the Ravens’ improvising and unsettled offense, Kansas City’s is finely tuned with a scheme built around quarterback Patrick Mahomes — and speed. A lot of it. Chiefs coach Andy Reid worked the Ravens with short timing patterns and crossing routes across the middle.

At times, the Ravens appeared to be over-coached, possibly caught up in all the hype surrounding the rematch of last year’s 17-10 AFC championship game loss.

The Ravens made adjustments in the third quarter but they were too slow, always a step behind Kansas City’s. Baltimore was fortunate that running back Isiah Pacheco dropped a would-be touchdown pass early in the second quarter. And again when running back Samaje Perine failed to handle a would-be 40-yard score in the third.

Where were the adjustments? Why weren’t these players covered?

The same question was asked when rookie wide receiver Xavier Worthy caught a 35-yard touchdown pass from Mahomes with 10:25 left to put the Chiefs ahead by 10. Ravens cornerback Marlon Humphrey seemed to expect safety help over the top, but there was none.

When those things happen, they stay lodged in the back of your head and come up when the Ravens continue to have problems. Some players aren’t getting the message.

Regardless of the coaching turnover, this is basically the same defensive group from a year ago that became the first in NFL history to lead the league in points allowed per game, sacks and takeaways.

The Ravens lost only three defensive starters during the offseason in linebackers Patrick Queen, Jadeveon Clowney and safety Geno Stone, yet, at the same time, this was the opener. Time to be ready. Baltimore played only a few starters during the preseason, and it showed.

They were playing against Mahomes, who has won two straight Super Bowls and played well, completing 20 of 28 passes for 291 yards. Now, if that happens this week against the Raiders and starting quarterback Gardner Minshew II, then it’s time to be less forgiving of Orr.

Minshew is no Mahomes, Antonio Pierce is no Reid and the Ravens are at home. This is Baltimore, not Charlotte, home of the Carolina Panthers. It’s a real home-field advantage.

“You have your floor and your ceiling. How high is the ceiling [and] how high is the floor?” Harbaugh asked. “You want to always raise the floor. That’s what winning football does — it raises the floor as high as it can be — we’ve been that kind of team over the years; that’s why we’ve won so many games. The Chiefs’ floor was higher in that game than ours was, and ultimately, that was probably the difference in the game.

“Those are the things that we can do this week — we can raise that floor up quite high. I’m not too worried about our ceiling.”

We’ll see.