Chris Cook wasn't familiar with NFL power rankings. So when a teammate recently told him about a Week 1 ranking that gave the Vikings very little credit, his first reaction was, "What's that?"

Which soon became: "What's this?"

"Everybody is sleeping on us," the Vikings cornerback said. "Apparently we're 26th and [San Diego] is No. 3. I was like, 'Whatever.'"

There was a smile, a bit of an eye roll. Perhaps a suggestion: Wait until Sunday.

What's that line about being careful what you wish for? The Vikings open the season at San Diego, consensus favorite to win the AFC West and owners of one of the most potent passing attacks in the NFL last season.

Philip Rivers is coming off a season in which he was second in the league in passer rating (101.8), first with 4,710 passing yards and fifth with 30 TD passes.

And the receiving corps is filled with guys who dwarf their competition. Vincent Jackson, back after a 2010 season marred by his holdout, is 6-5. So is Malcom Floyd. Antonio Gates is a dominant tight end at 6-4. And the running back combination of Ryan Mathews and Mike Tolbert looks to be formidable.

"[The Chargers] are a challenge for any defense, let alone coming off what we're coming off from a health standpoint," Vikings coach Leslie Frazier said. "Terrific receivers, terrific quarterback. No. 1 offense from a year ago. We'll find out where we are, early on.''

The Chargers have an aggressive style, a smart, quick-thinking quarterback and all sorts of weapons to which to throw. The Vikings, meanwhile, have two cornerbacks coming off knee injuries in Cedric Griffin and Cook, and continuing questions at safety.

"They're explosive," said veteran cornerback Antoine Winfield, generously listed at 5-9. "All their receivers are 6-4 or better. ... I'm sure we'll be up to it."

Of course, that has to be the belief. But, at the very least, it is a heck of a difficult start for a secondary still coming together.

Winfield and Griffin -- who is coming back from a second torn anterior cruciate ligament that limited him to two games last season -- are the starting cornerbacks. Cook, the nickel back, sustained torn cartilage in both knees that limited him to six up-and-down games as a rookie last season. Even Frazier said the coaches were waiting to see exactly what they have, even though Frazier knows the potential of the group, referencing the one game last year -- a home victory over Detroit -- in which all three were on the field together.

Neither Griffin nor Cook -- who nursed a sore hamstring in camp -- saw extensive action in the preseason. At strong safety, Jamarca Sanford and Tyrell Johnson went through camp battling for the starting job before Sanford emerged by a nose.

The Vikings, reacting to injuries all season, finished 22nd in pass defense in 2010. Now their top three corners are healthy for the opener, but have they had enough time together?

"I talk to Antoine all the time about that," said Cook, who plays outside with Winfield moving into the slot in nickel situations. "We can go out and be the best three [cornerbacks] in the league if we all do what we can do."

Given the San Diego approach, the Vikings could be forced into some sets with six defensive backs. In that case, Marcus Sherels likely would be the final extra back, lining up in the slot. At the very least, the Vikings figure to be in nickel better than half the time.

One thing is for sure. The team will know a lot more about its defensive backs after this game.