Percy Harvin ignites, Christian Ponder commands and Adrian Peterson powers the offensive assembly line that has produced enough points for four attention-grabbing victories. But fueling the Vikings’ revival has been their defense.

Robust against the run and swinging a big stick in the secondary, the same unit that was savaged last season suddenly is among the finest in the NFL, thanks in large part to the big-tent philosophy espoused by first-year coordinator Alan Williams, the even-tempered boss of the team’s most charismatic bunch.

Somebody has to harness the talents of supersized characters like Jared Allen, Brian Robison, Everson Griffen and Jamarca Sanford, the last of whom could be heard chirping at opponents from across an airport runway.

Williams has been an ideal match for coach Leslie Frazier’s defense. He tweaked rather than trashed the Tampa-2 coverage scheme, began rotating interior linemen to leverage Minnesota’s depth and welcomed player feedback instead of marginalizing the help.

“I think what it comes down to is players not letting egos get in the way, coaches not letting egos get in the way,” Robison said Monday, Oct. 8. “He’s done a great job of understanding what his players are comfortable with and trying to compromise and find a way that we can both get done what we need to get done, and it’s resulting in wins so far.”

Last year, the Vikings’ defense was a disaster on and off the field.

Cornerback Chris Cook was jailed on a domestic violence charge of which he ultimately was acquitted but not before missing the final 10 games. The rest of the secondary was ravaged by injuries. Defensive coordinator Fred Pagac failed to connect, and Frazier was forced to take over some play calling after some players bucked assignments.

Williams spent 10 years coaching defensive backs with the Indianapolis Colts and won a Super Bowl with Frazier in Tony Dungy’s regime. His graciousness and understanding is a by-product of that shared experience, a business-like approach that resonated with a defense desperate for success.

“It can be tough if you’re coming into a locker room with a lot of old vets, guys that have been in the league, and they really know everything or think they know everything,” Sanford said. “Here, we just bought into whatever he brought and didn’t question from Day 1 was he the guy or not or what he brings to the table. Just bought in, believed. Anything you put your mind to you can do.”

Through five games the Vikings rank sixth in points per game (15.8) and run defense (78.6 yards per game), seventh in total defense (304 yards per game) and tied for eighth in sacks (14). Moreover, their much-maligned pass defense respectably ranks in the middle of the pack.

The offense continues to progress and gain confidence as Ponder keeps the chains moving, Peterson returns to normal and Harvin stakes an early claim on the MVP award.

But the defense likely will determine whether the Vikings can maintain momentum and compete with offensive juggernauts Green Bay and Chicago, which await them four times in the second half of the season.

“I’ve seen it as a player, and I’ve always believed it as a coach as well,” Frazier said. “(If) you’re not playing good defense, in my mind, it’s just hard to win in our league. And I know there are some teams that buck that a little bit, by putting up a lot of points and a lot of yards.

“I just think in the long term, to be good in our league for a long period — and that’s what we’re hoping to be able to do, not just be a one-year wonder or a two- or three-game wonder; we want to be a football team that is good for a long period of time — you have to play good defense. We’re doing that right now. And, the results are, we’re on the upside.”

The Vikings are 4-1 following their strongest defensive performance of the season Sunday in a 30-7 whipping of the downtrodden Tennessee Titans, who were held to about 90 yards of total offense through three quarters before stitching together a couple of meaningless drives when the game was out of hand.

“The defense is playing huge,” Harvin said. “I said after the game, especially at halftime, I told the ‘D’ we owe ’em. Last week and definitely this week just past, they kept us in the game big time. If our offense can catch up to where our defense is playing right now, we’ll be all right.”

For now, the defense’s biggest challenge seems to be loosening up its buttoned-down coordinator.

Robison and his free-spirited colleagues have tried in vain to draw out Williams, who rarely betrays emotions on the sideline even during the heat of battle.

“He told us straight, ‘I’m not a rah-rah guy, you’re not going to get that out of me,’ ” Robison said. “Maybe by the end of the year he will be a different Alan Williams.”

In reality, there is very little the Vikings would change.

“He’s one of those guys that if you are doing something bad, he’s going to pull you to the side and tell you; he’s not going to embarrass you,” Robison said. “At the same time, if you do something good, he is going to let everybody know about it. He’s just a good coach. He’s kind of a players coach and we like him, and we like the things that he’s doing.”

Follow Brian Murphy on twitter.com/bmurphPiPress.