MINNEAPOLIS -- On Sunday, Mike Zimmer will begin his third season as the Minnesota Vikings' coach, facing the last team that told him it wasn't going to hire him.

Zimmer had interviewed for the Tennessee Titans' coaching job in January 2014, only to be passed over in favor of Ken Whisenhunt. The experience was disheartening enough that Zimmer briefly thought about declining a second interview with the Vikings, in the interest of sparing himself another round of rejection.

Two years later, Zimmer is coming off an NFC North championship and working with a new contract, having gone from a frequent runner-up in coaching searches to one of the more well-respected new coaches in the game. He's gotten there by putting his imprint on a defense that, before Zimmer was hired, allowed more points than any in the league. Now, in their third year under Zimmer, the Vikings aim to have the kind of defense that can carry a team to a championship.

Nine of the Vikings' 11 defensive starters have been with the team since Zimmer became the coach. The starting unit includes four players the Vikings selected in the first round, and one more they took in the second round. The group returns all 11 starters, and a handful of key role players, from a team that gave up the fifth-fewest points in the league. And the Vikings' defenders have learned to conform to the exacting standards of a coach who isn't all that impressed by any of it yet.

"I think we’ve still got a long way to go. My expectations are pretty high all the time," Zimmer said Monday. "I don’t like to give an inch, so when we do, I get upset about it."

The Vikings could be asking more of their defense after the season-ending knee injury to quarterback Teddy Bridgewater, and players have drawn confidence in training camp by the continuity that comes from three years in the same scheme. Still, there are some obvious areas of improvement the Vikings must make if they want to go from a good defense to an elite unit.

Essentially, the team was at is best creating pressure last year, especially in the red zone and to get off the field on third downs. Only two teams in the league created more third-down pressure than the Vikings did last year, according to ESPN Stats & Information, and only five pressured quarterbacks more frequently in the red zone. The Vikings only brought extra pressure 26.6 percent of the time, but Zimmer's vaunted double-A gap blitz package helped the team become the most effective blitzing defense in the league, with pressure on 49.4 percent of dropbacks with five or more pass-rushers.

The Vikings, though, could stand to be better against the run, where they ranked only 17th last year. Zimmer's charges often repeat his mantra about how sound run defense sets up the right to rush the passer, and last season the Vikings allowed the seventh-highest average carry on first and second downs. Should the Vikings get better at keeping their opponents in third-and-long situations, they could create even more pressure this year. "You stop the run, you get them in third-and-long situations and now we get to talk about [pressuring the quarterback]," defensive end Everson Griffen said Thursday.

That could also lead to more takeaways -- which Zimmer has made another area of emphasis before this season. The coach is careful not to stress turnovers at the expense of sound coverage principles, and often tells his cornerbacks their first responsibility is not to let their man catch the ball. A group that is well versed in the coach's system, though, could find room to pursue more interceptions without cheating in coverage.

"If we could get into some second-and-12s, that helps doing some of those things instead of second-and-5s," Zimmer said last month. "The first downs are going to be important for us. With them, whether it be the different types of passes on first down or the running game, if we can get offenses into more manageable situations for us, I think that will help create more turnovers."

The ingredients are there, though, for an elite defense. The Vikings have a unit full of athletic, flexible players who know their responsibilities and when they have freedom within the structure of the defense. An opportunity exists for the group to become dominant. And with the quarterback situation in flux, another step forward from the Vikings' defense could deliver a surge to the whole team.