Not too long ago, the Vikings seemed poised to join the pantheon of the greatest defensive teams of all time. Around these parts, as Mike Zimmer’s defense carried the Vikings to a 5-0 start, the only thing worth debating was whether the 2000 Ravens, 1985 Bears or Steel Curtain Steelers should be second on the list.

The Vikings scored a pair of defensive touchdowns to single-handedly win the season opener. They started the latest “What is wrong with Aaron Rodgers conversation?” They pummeled Cam Newton, another superstar quarterback. They made DeAndre Hopkins disappear and Odell Beckham Jr. throw another temper tantrum.

Even in a double-digit loss in Philadelphia, their defense played well enough to win, forcing four turnovers and limiting the Eagles to 239 yards of total offense.

But since then, glimpses of greatness have been sparse. More often, the Vikings defense looked closer to average as pressure mounted to halt the team’s slide.

Eager to produce more big plays to prop up an underperforming offense that is now three weeks removed from a coordinator change, the defenders, including some of the team’s brightest stars, are now chasing plays instead of staying within the scheme. As a result, Zimmer’s tight-knit defense has begun to unravel. That group needs to bind back together to keep the slumping team’s playoff hopes from fading further.

“We’ve just got to get back to being us,” cornerback Captain Munnerlyn said. “I feel like we’ve been playing poorly, because when the team needed us to step up, we didn’t. The first five weeks, any time we needed to get off the field or get a turnover or make a big play, we did. The past few games we haven’t been doing that.”

He added: “I don’t know if we’ve been pressing too hard or if guys have been trying to do other people’s jobs. We’ve just got to get back to being one of 11.”

Empty effort

Statistically speaking, aspects of the incredible start were likely unsustainable. The Vikings forced three turnovers in each of their first three games, and after burying Newton eight times in Week 3, they were on pace to shatter the NFL sack record.

That early success might have emboldened some defenders, with the offense struggling to score touchdowns, to try to vacate their positions in search of more big plays.

“We had some games where we got a bunch of takeaways, a bunch of sacks and a bunch of stops,” cornerback Terence Newman said a day after the 26-20 loss in Washington. “Then guys try to keep doing that and they try to press and do too much. And you start to do things that create seams and create gaps and whatnot.”

Matt Bowen, a former NFL safety who played for four teams, said that is “natural.”

He recalled his 2004 season with the Redskins, the year that Joe Gibbs returned to coach the team. That defense finished the season in the top five in both scoring and yards allowed. But there were lapses as individuals tried to overcompensate for a Redskins offense that ranked in the bottom three in points and total offense.

“It’s tough when your offense is struggling,” said Bowen, now an analyst for ESPN. “There’s no doubt about that. Because you’re on the field a lot more and you’re put in more adverse situations when you’re dealing with plus field position for an opposing offense. There were times when all of us were pressing a little bit.”

When watching the Minnesota defense, which he felt after six games was capable of carrying a team to the Super Bowl like the Denver defense did last season, Bowen believes that some of the Vikings defenders are indeed pressing a little bit, too.

He pointed to a 25-yard reception by Redskins tight end Jordan Reed in the first quarter of last week’s loss. He noticed that safety Andrew Sendejo, who has picked off two passes and recovered a pair of fumbles this season, got caught peeking into the backfield, which allowed Reed to get outside leverage on a corner route.

“It’s just the little things that are starting to show up with that defense that can multiply when you start stacking them together,” said Bowen, who retired in 2007.

Fear is gone

The Vikings allowed a league-low 13 gains of 20 or more yards during the first six games of the season. They have been victimized for that many in the past three games, with missed tackles playing prominent roles in six of those explosive plays, including the game-winning touchdown pass in an overtime loss to Detroit.

The Vikings have whiffed on at least 10 tackle attempts in each of the past three games, per Pro Football Focus, after wrapping up opponents so well early on.

The missed tackles have led to cracks in a run defense that had been stouter early in Zimmer’s third year as coach. The past three games, their opponents have rushed for a total of 383 yards, 69 of them coming on a run by Bears running back Jordan Howard in Week 8, after safety Harrison Smith missed him in the hole.

“We got hit on a couple of plays,” Zimmer said. “I’m really not concerned about it.”

With their run defense springing leaks the past three games, the Vikings have been in fewer third-and-long situations. But no matter the distance to the sticks, they have had trouble getting off the field. They were below the NFL average on third-down stop rate on third-and-short, -medium and -long, per Pro Football Focus.

They have been blitzing just as much as they did during their first six games, sending five or more defenders a third of the time, according to Pro Football Focus, and they have generated pressure on the quarterback at about the same frequency. But with only seven sacks in the past six games, their rushers are rarely hitting home.

“If you look at the Green Bay film, the Carolina film and the Giants film, they were creating panic on almost every down. Those quarterbacks were panicking … and looking for ghosts in the pocket,” Bowen said. “You’re not seeing that as much.”

That is in part because opponents have been relying on quick throws to neutralize the pass rush. Each of the last six quarterbacks the Vikings have faced got rid of the ball at an average of 2.53 seconds or less, according to Pro Football Focus. The quick completions coupled with missed tackles have resulted in 53.4 percent of opponents’ passing yards coming after the catch, one of the NFL’s highest rates.

“They’re getting the ball out. We’re going to have to adjust how we do some things with the pass rush. We’re going to have to adjust [our coverage to] take advantage of that,” Zimmer said. “Every year you go through this. This isn’t anything new.”

Players haven’t changed

Bowen believes the Vikings, who despite their recent struggles are still ranked first in the NFL in scoring defense, aren’t far from regaining their early-season form.

“You’re talking about the same players,” Bowen said. “And the key is that those guys were hand-picked for that scheme. And they have one of the best coaches in the NFL in Zimmer, and I think they’re still in a position where they can make a run.”

But the Vikings are being reminded of just how difficult it is to sustain week-to-week success in the NFL, with injuries popping up and matchup nightmares most weeks. That is what made those great Ravens, Bears and Steelers defenses, well, great. Ditto for the current Seahawks defense as it shoots for its fifth straight scoring title.

“The really great defenses, when an offense is not carrying as big of a load as some might expect, the really great defenses take pleasure in that,” said former NFL head coach Mike Nolan, who is now an analyst for SiriusXM NFL Radio. “They know it’s up to them to shut the opponent out [every week], and they take that responsibility.”

Nolan, like Bowen, believes there is nothing wrong with Zimmer’s scheme, though the Vikings coach did admit to “trying to do a little too much,” too, with his play-calling.

“It really comes down to the good players performing at a higher level within that scheme,” Nolan said. “It still starts with the players when it comes to how good they’re going to be. They need to take it upon themselves to make everything work.

“Maybe they’re not quite as good as everyone thought they were. But I still think they’re a pretty doggone good defense. They’ve just kind of hit a little lull here.”