Video (01:58) : The Metrodome is now completely at ground level after the least seating bowl support was demolished Saturday.

The Vikings used the first week of free agency to reduce their desperation at quarterback and give their defense a fighting chance on third downs.

The former buys time and affords the team better draft judgment, knowing that Matt Cassel, while not ideal in age and consistency, is far better than overreaching for the wrong quarterback for the second time in four years.

“I think that was a huge piece to this whole thing,” said General Manager Rick Spielman, referring to the March 8 re-signing of Cassel. “That got us going in the right direction.”

With Cassel on board, the Vikings shifted their attention to a defense that ranked last in points allowed (30.0 per game) and 31st in total yards (397.6) and passing yards (287.2). And as anyone who followed the team last year knows, the root of all that rot was a 30th-ranked third-down defense that allowed teams to convert at a 44.2 percent clip.

Re-signing end Everson Griffen and adding nose tackle Linval Joseph and cornerback Captain Munnerlyn adds three starters under the age of 27 to a defense that had grown too old. Joseph and Munnerlyn are instant upgrades. Griffen is supremely talented and versatile, but belief that he’s an upgrade in 2014 still requires a leap of faith that he’ll be better entering the prime of his career than Jared Allen was near the end of his.

Munnerlyn, 25, was so sold on the direction of this defense that he predicted a top-10 ranking once Spielman and new coach Mike Zimmer are finished restocking. And that’s saying a lot considering that Munnerlyn was present for perhaps the most embarrassing defensive performances of the 2013 season.

Re-signing Matt Cassell allows the Vikings not to reach for a quarterback.

It was Week 6 and the Vikings were coming off a bye week and their first victory of the season. And they were at home against a Panthers team that also was 1-3.

Final: Panthers 35, Vikings 10.

Panthers quarterback Cam Newton posted a career-high 143.4 passer rating while the Panthers went 7-for-12 (58 percent) on third down and 2-for-2 on fourth down.

Munnerlyn shrugged when asked about what he saw in the Vikings defense that day.

“It was just in the back end [of the defense],” he said. “I think we’ve just got to make more plays on the ball, and I think that’s why they signed me. I’m sure they’ll sign more guys or bring some more guys in. But it’s just making plays on the ball and getting off the field on third down. That’s the key.”

The Vikings took the inability to get off the field on third down to a comical low not long after the Panthers left town. On Oct. 27, the Packers converted 13 of 18 third downs (72 percent) and two of two fourth downs while going the entire game without a punt.

After the Vikings won their next home game to improve to 2-7, then-coach Leslie Frazier was asked, jokingly, what was going through his mind when his defense finally stopped someone on third down.

Frazier smiled, pumped both arms above his head and said, “I was like, ‘hooray, hooray, hooray.’ ”

Despite going 4-3-1 in the second half of the season, Frazier was fired before he could reap the personnel upgrades from the past week and going forward.

Joseph, a run-stuffer with deceptive pass-rushing skills, is the team’s first legitimate nose tackle since Pat Williams was setting the tone for the league’s best run defense. And for those who don’t think a gap-eating nose tackle helps on third down, let us point out that third-down situations are set up by what happens on first and second down. For example, 11 the Packers’ 18 third-down situations last Oct. 27 were 3 yards or fewer. They converted nine of them.

Munnerlyn, meanwhile, has the same skill set that Frazier was pleading for behind the scenes when Antoine Winfield was interested in coming back during the early-October bye last year. Like Winfield and no one the Vikings had in 2013, Munnerlyn is adept at starting outside and then sliding over the slot receiver in the nickel defense. A huge piece to any third-down defense.

Having filled all the major holes they had entering free agency just a week ago, the Vikings appear better defensively and most certainly are in position to stay true to their draft board come May.

That’s good because the last time they weren’t able to do the latter was 2011, when the NFL lockout prevented free agency from starting before the draft. With Brett Favre retired and no viable options to replace him, the team ended up taking Christian Ponder 12th overall. And that, the Vikings discovered, is a good enough reason to avoid being boxed in on draft day.