The Cincinnati Bengals were more than good Sunday, but they didn’t ruin Robert Griffin III’s home debut for the Washington Redskins. No. This was an inside job, perpetrated by the very people who were supposed to have their rookie quarterback’s back, committed by the one unit Mike Shanahan “thought was going to be the strength of our football team.”

It’s 4 p.m. Sunday, Washington. Do you know where your defense is?

Getting scored on. Again.

“You can’t go out and ask a rookie quarterback to put up 40 points every week,” Lorenzo Alexander said early Sunday evening after his teammates had cleared out of the locker room. “Thirty-plus points the last three games — we’re not going to win too many games that way. We got to do something.”

London Fletcher described the Redskins’ lousy performance against Cincinnati as “extremely frustrating.

“Defensively we thought we’d be a better unit, and I know we will be,” the defensive captain said.

For the first time since 2005, the Redskins have scored 99 points in three consecutive games combined. But when you give up 101, that still leaves you with a losing record.

A week after surrendering 452 yards to the Rams, the Redskins gave up 478 yards to the Bengals. This sun-spackled day in Landover seemed destined to end with a stirring Griffin-led second-half comeback — that is, until Jim Haslett’s guys couldn’t stop Andy Dalton, A.J. Green or, really, anybody else when it mattered.

The Bengals had six plays of 25 yards or more: three long touchdowns, including a 73-yarder to Green on the first play from scrimmage that dampened the festive spirit before the game was a minute old. That the touchdown came on a trick play — on a pass from reserve wideout Mohammed Sanu — just seemed to rub salt in the wound.

If anyone thought this was an anomaly, it would be one thing. But we’re going on two years now of opponents exploiting a Cover-Zero scheme that lives up to its name: DeAngelo Hall and friends really don’t end up covering anybody.

For the eighth straight game dating from last season, Washington gave up more than 31 points and more than 350 yards. That’s got to really irk the loyalists who waited so long and patiently for an offense to emerge: Now that it has, the holes that need to be patched are on the other side of the ball.

“We felt like we knew what they doing going into it by the way they were playing,” Dalton said after throwing for 328 yards and three touchdowns. “For us, it was just about taking advantage of it.”

I asked Orson Charles, the third-string tight end on the Bengals, what he saw. “On a couple of the big plays, when the Redskins were playing us in a double tight-end set, we saw a lot of man-to-man coverage and Cover-1 that we just exploited.”

Added Green, who shrugged his shoulders when asked if any of the Redskins’ defensive backs gave him problems, “I guess they confident in their corners.”

After watching Josh Wilson embarrassed along the sideline by Bengals receiver Armon Binns for a 48-yard touchdown, you wonder where that confidence comes from.

It would be one thing if the Redskins were only getting beaten off the edge; they’re not.

“It’s disappointing,” Shanahan acknowledged. “I thought the defense was going to be the strength of our football team, and even though it doesn’t look that way to start off, we lost a number of our guys and we are starting to regroup . . . we have more depth than we had in the past. There are no excuses for us not to get better. We just didn’t do it today.”

After falling behind 24-7, Griffin and the offense knotted the score at 24 with less than 4 minutes left in the third quarter. The stadium shook with sound. The defense even forced consecutive three-and-outs against Dalton, shoring up holes.

And then Dalton went to work again — and it was over.

(Okay, it wasn’t completely over. The Redskins drove the length of the field late, but apparently Kyle Shanahan got too mouthy with a replacement official at the end, and the Redskins were penalized big yards. Funny, no, that Josh Morgan faced the music last week after his loss of composure, but the offensive coordinator was uncharacteristically unavailable to the media after Sunday’s game. Come on, Kyle, you’re better than that.)

With New Orleans falling to 0-3, that opening-week upset doesn’t look as grand anymore, does it? Don’t blame Griffin, who is as good as advertised. It’s just a shame he has to play catch-up with the way this defense is consistently underperforming.

It would be easy to give the Redskins an excuse after last week’s season-ending injuries to Brian Orakpo, their most fearsome pass-rusher, and Adam Carriker, one of their best space-eaters on the defensive line. But then you see what the Giants did to Carolina without four offensive starters during a short week, and you know that alibis only go so far in the NFL.

Griffin is having a hard enough time just staying upright. Like all young quarterbacks, he has become a target. The Bengals marveled at how much punishment he could take while rising for another snap after every crunching collision.

The least the defense could do for him is contain the other guy’s quarterback. Griffin can run, pass and play maestro with the football in the backfield — but he can’t play cornerback too.

Let’s not get carried away and start the “Has’ Must Go” chant. But the recently extended Jim Haslett and that unit need to officially be put on notice after Sunday. Giving up nearly 1,000 yards in back-to-back weeks is not acceptable. Giving up big plays like the ones the Bengals racked up should do nothing for anyone’s job security.