The criticism that has beset the Vikings following a pair of opening losses hasn't crushed the vibe in their locker room.

While some fans scream "fire," the Vikings say they aren't even smelling smoke.

That mantra is maintained by members of a defensive backfield who seem far more focused on "playing our game" than worrying about the suddenly imposing Detroit offense.

The Lions, led by quarterback Matthew Stafford, have the sixth-ranked passing offense in the NFL, Stafford has the fourth-best passer ranking, and receiver Calvin Johnson already has four touchdown receptions.

But the Vikings secondary said its main objective in Sunday's meeting will be to finish as strong as it starts.

"They're playing some good football over there. But at the end of the day, it's about us," free safety Jamarca Sanford said. "We just go out and keep doing what we're doing. And play for four quarters."

That Vikings have struggled mightily in the second half of both their games, blowing double- digit leads at San Diego and against Tampa Bay at the Metrodome. The offense has basically been three-and-out in second halves, but the defense has given up an average of 183 passing yards after halftime. Opposing offensive coordinators and players have recognized vulnerabilities in the Vikings' second-half defense and taken advantage.

Stafford and Johnson present the most explosive tandem the franchise has faced this season. Stafford, a former No. 1 choice plagued by health issues during his first two seasons, is precise, and now he's protected -- he hasn't been sacked this season.

The Vikings secondary is charged with limiting Stafford's options.

"He does a lot of good things, but I think it's mainly about what we do," strong safety Husain Abdullah said. "As long as we do what we do and we're right, then we'll be OK."

Defensive coordinator Fred Pagac said the secondary alone can't take blame for the woes of a defensive unit that has lost momentum down the stretch of its first two games.

"No. The 11 players have to make better adjustments as far as just playing football," Pagac said. "Same calls we played in the first half, we played in the second half. For whatever reasons, we didn't get the job done."

More misfires Sunday, especially in the defensive backfield, likely would cost the Vikings again.

The alley-oop to the 6-5 Johnson in the red zone -- and everywhere else on the field -- usually works. Pagac said the Vikings will throw different packages at the Lions to pressure Johnson and attempt to limit his production.

But cornerback Cedric Griffin said Johnson, whom he called a "premier athlete," only represents a piece of the Lions' potent attack and shouldn't be the only player who faces scrutiny.

"We don't look for one player on the roster and try to defeat him," he said. "We try to defeat all 53 players on the team."

The secondary members charged with avoiding more second-half challenges in the future said they believe they're equipped for the task, if they play together and consistently.

"It's about really going out and playing one defense," Sanford said. "As long as we do that it really doesn't matter who's on the other side of the ball."