MINNEAPOLIS -- The last time the Minnesota Vikings faced the New York Giants on Monday Night Football, they slunk out of MetLife Stadium following one of the most embarrassing quarterbacking displays in the franchise's six decades.

Josh Freeman, signed 15 days before the game, completed only 20 of his 53 passes for 190 yards and an interception, in what would be his only start in a Vikings uniform. The Vikings did not score an offensive touchdown in a 23-7 loss to the previously winless Giants in that 2013 game, falling to 1-5 a year after they'd earned a surprising wild-card berth. Owner Zygi Wilf gave a vote of support to coach Leslie Frazier on his way out of MetLife Stadium that night, but if a disheveled quarterback situation hadn't yet sealed Frazier's fate, the performance of an undermanned and outmoded defense probably already had.

The Vikings allowed 480 points that season, the second-most in franchise history, and frittered away last-minute leads in five different games, finishing 5-10-1 in a year when the Green Bay Packers needed only eight wins to claim the NFC North title.

Cornerback Josh Robinson flailed in his only turn at slot cornerback, following the surprising release of (and aborted effort to re-sign) veteran Antoine Winfield. Second-year safety Harrison Smith missed half the season with turf toe, while rookie corner Xavier Rhodes was miscast in the Vikings' stale Cover 2 scheme. Linebacker Erin Henderson was out of place in the middle of the defense, before a November arrest cost him his starting job. The team's veteran linemen chafed at defensive coordinator Alan Williams' passive approach at the end of games. And six days after the Giants loss -- as Packers quarterback Aaron Rodgers directed a masterful Sunday night performance in which Green Bay didn't punt once -- NBC's cameras caught defensive end Jared Allen mouthing, "I've never played on a defense this bad in my life."

Three years later, as the Vikings prepare for a Monday night showdown with the Giants two weeks after a Sunday night game against the Packers, they've again shuttled through quarterbacks, once more starting a quarterback 15 days after they acquired him following Teddy Bridgewater's catastrophic knee injury on Aug. 30. They've placed Adrian Peterson and Matt Kalil on injured reserve. And yet they're bidding for a 4-0 record because of a defense that no longer has the terms of a game dictated to it.

The transformation of the Vikings' defense, from milquetoast to menacing, has been as deliberate and purposeful as it has been striking. It began with general manager Rick Spielman's decision to replace Frazier with Mike Zimmer, who quickly tore the defense down to the studs, changing everything from the scheme to the coaches to the way players met.

The first player Mike Zimmer and the Vikings scouts drafted in 2014 was linebacker Anthony Barr. Robin Alam/Icon Sportswire

Zimmer walked the team's scouts through video of the defenses he'd directed in Cincinnati, detailing the tasks players would perform and the body types he wanted. The Vikings made the decision to keep defensive end Everson Griffen, making a $42.5 million bet the talented defensive end would develop into a stout run defender and formidable pass rusher alike. They plugged holes in the middle of the line and in the secondary by signing nose tackle Linval Joseph and slot cornerback Captain Munnerlyn, and they spent their first 2014 draft pick on Anthony Barr, the converted running back whom they believed would become the knife edge of Zimmer's 4-3 defense.

After 2½ years, a total of six defenders selected in the first three rounds and three starters added through free agency, the Vikings have a defense that has become one of the best in the league, both modernized to fluster the NFL's best quarterbacks and rooted in time-tested principles of collectivism, attention to detail and resiliency.

The group, which allowed the fifth-fewest points in the league a year ago, is third this year, having become just the third team in NFL history to beat the past two NFL MVPs in back-to-back games. Only two teams have pressured quarterbacks more frequently this season; none have sacked passers as regularly. A coaching staff that refused to prioritize turnovers over sound technique now has molded a group that ranked second in the NFL in takeaways through Week 3. And while the Vikings' 2013 defense couldn't buttress the team against winds of uncertainty on offense, the 2016 group hasn't been fazed by them.

"It's hard to imagine I'm still here through all that, I guess," said linebacker Chad Greenway, the team's longest-tenured player who remains the conscience of the Vikings' defense in his 11th season. "You can kind of see the transition in the mentality, I would say. I think that comes from Rick on down through Zimmer and his staff, the way they're coaching us and the way they're putting us in position to make plays. Yes, we have good players, and we have guys that are playing hard. But we're in position to make plays, too. They're doing a great job coaching us."

Building a foundation

The transformation began in the early days of 2014, after the Vikings fired Frazier and started what turned out to be a 2½-week search for a head coach. Spielman's hunt took him to Zimmer, who'd built his reputation as a defensive technician, and Zimmer worked through a short list of coaches who'd already established themselves in the league.

He hired Miami linebackers coach George Edwards, who'd previously been a defensive coordinator in Buffalo, to be his defensive coordinator in Minnesota. Another former coordinator, Jerry Gray, was brought on board as the defensive backs coach. Zimmer added his longtime colleague, Andre Patterson, to lead the defensive linemen, and brought his son Adam over from his staff in Cincinnati to coach linebackers.

The next step was finding players who could fit the scheme. The Vikings' defensive front would be built with linemen who could play the run on their way to the quarterback, occupying blockers and collapsing pockets rather than immediately penetrating the backfield. That meant veterans like Allen and Kevin Williams would be moving on. Griffen and Brian Robison could fit, but both would have to play their position differently. So, too, would Greenway, who went from Frazier's Tampa 2 defense to a scheme that asked linebackers to run and hunt.

The Vikings also needed some muscle for Zimmer's double-A gap blitz package, which would be the foundation of how the team would get after quarterbacks. The pre-draft process led them to Barr, who'd been projected to play outside linebacker in a 3-4 scheme but could become a versatile weapon as a strong-side linebacker for Zimmer, much as James Harrison had been in the Bengals' 4-3 scheme in 2013.

"One of Zim's strengths is the ability to identify what he sees as positives and weaknesses in a player, and how he's going to utilize the positives to fit what we do, but also to adjust what we do," Spielman said this summer. "One of the big examples of that was in our first draft together with Anthony Barr, who people didn't think was going to be a fit here. We've been together for three drafts now; we have a pretty good understanding of what he's looking for, and he has a very good understanding of our process. Communication is the whole key."

Zimmer began his NFL career working with Deion Sanders as the Cowboys' defensive backs coach, and there might not be a position closer to his heart than the secondary. He ran Rhodes through an intensive indoctrination to his coverage techniques, repeating the process with first-round pick Trae Waynes a year later and second-round pick Mackensie Alexander this year. Munnerlyn, after a 2014 season where he admittedly freelanced too much, adapted to the scheme in 2015. Terence Newman was brought in for his third tour with Zimmer before 2015, as a starting left corner and a steadying force for the group.

The underlying message of the defense was simple: The techniques work, if you play them correctly.

"I think it kind of goes back to having us play fast," said Smith, who made his first Pro Bowl last season. "I think all the coaches do a great job of saying, 'Here's our technique -- go out and play it.' If we don't play fast or we can't do it exactly how they envisioned it, they might just be like, 'We're not going to do it.'"

Minnesota's overhaul on defense began with the hiring of Mike Zimmer in 2014. Adam Bettcher/Getty Images

Graduate-level blitzes

The Vikings return all 11 starters from last year, and have eight who are in at least their third year in the scheme. If three years spent under the exacting tutelage of Zimmer's staff has helped the Vikings master the basics -- through three weeks, they were tied for the second-fewest plays allowed of 20 yards or more -- the continuity has also helped them graduate to more complex levels of the defense.

Zimmer has never been known as a heavy blitzer; his defenses in Cincinnati ranked 20th in the league in blitz percentage from 2008-13, according to research by ESPN Stats & Information, and his first two Vikings teams were 18th and 20th. Through the first three weeks of the season, though, the Vikings had blitzed on 34.6 percent of dropbacks, which was the third-most in the league.

Game situations certainly dictated some of the pressure, but given the fact the Vikings have played three mobile quarterbacks in Marcus Mariota, Rodgers and Cam Newton, it's probably safe to assume Zimmer wouldn't be calling for extra pressure if he didn't think his players could handle it.

"I think it’s sort of been a steady increase from year to year," Edwards said. "Knowing our personnel better, the players that we’ve added, trying to use their skill sets within the different packages, I think it’s a culmination of all those things coming together."

The Vikings rushed a defensive back on just 48 snaps all last year, according to research by ESPN Stats & Information. Through three games this year, they'd done it 17 times, which was tied for seventh in the league. The fluidity of the group is what makes it so lethal.

"I love Mike Zimmer's blitzes. I think they're some of the best in the league," said ESPN's Matt Bowen, who spent seven season in the NFL as a safety for four teams. "Carolina struggled with it; they had protection busts. You don't know who's coming and who's going. Is Barr going to drop out? Is [Eric] Kendricks going to drop out? Is Harrison Smith going to drop out? Now, all of a sudden, they're coming, and you've got a free rusher off the edge. On [Terence Newman's] interception last week, I think it was Everson Griffen -- no one blocked him. He ran in and hit Cam Newton in the back. That's what you want. That's why you do those disguises, to make the offense break. I mean, I could watch Coach Zimmer's blitz schemes all day."

While Zimmer is among the early adopters of the double-A gap blitz, he probably isn't the father of it -- that distinction goes to late Philadelphia Eagles defensive coordinator Jim Johnson. Few have run it with more precision, though, and few have compiled a group of players who can cover enough ground to hold up in coverage the way the Vikings can.

"Think about it," Bowen said. "I think it was on the [Newman] interception: Anthony Barr drops out. He's immediately going to run under an inside route. He can get there faster than anyone else. Harrison Smith can drop out right over the tight end. The tight end's gone -- erase him. He's out of the play, too. Now there's two immediate reads that are gone. Now the quarterback's got to double-clutch, move his eyes. You don't have time for that. You can run that double-A gap blitz in the Turkey Bowl against your cousins and your uncle, and it's probably not going to look the same. But when you have the players in there -- if you bring Anthony Barr and Harrison Smith to your Turkey Bowl game, you're probably going to have some success."

The Vikings' continuity has expedited the group's ability to fix things that aren't working during a game, and it has even allowed Zimmer to go off-script from time to time. During the Vikings' Sept. 18 win over the Packers, the coach realized he had a pressure package that would work well against Rodgers. Problem was, the Vikings hadn't practiced it during the week.

"I went over and talked to the guys and said, 'Hey, you guys good with this?'" Zimmer said. "And they said 'yes,' so we ran it."

The Vikings are reaching the advanced levels of their defense, the ones where they go through their scheme with an effortless virtuosity from time to time. They're not flawless, as their first-half hiccups in Tennessee and Carolina will attest, and Zimmer isn't about to let them think they are.

"We have good players that are good team guys," he said. "They care about doing things right. They’re competitive, they’re smart. We definitely have not arrived. I think that it’s a long season; we have to continue to play good."

The Giants game, though, is as good of a milestone as any, given how much more adroitly the Vikings' defense has allowed them to handle the kinds of situations that felled them three years ago.

"The way they're playing right now, you're going to have to come in with a really good game plan to beat them," Bowen said. "The last two weeks, against two of the best teams in the NFC, we haven't seen it."