This wasn't the start that either Asher Allen or Chris Cook had envisioned.

Given the opportunity to play with the first-team defense in the Vikings' preseason opener Saturday at Tennessee, the young cornerbacks both had plays they immediately wanted back.

Allen failed to tackle fullback Ahmard Hall on the Titans' opening series, turning what should have been a short gain into a 10-yarder. On the next play, wide receiver Lavelle Hawkins got past Allen and caught a pass that went for 20 yards.

Cook missed a tackle early and then gave up a 45-yard touchdown to wide receiver Yamon Figurs in the second quarter when Jake Locker initially fumbled the snap and Cook let Figurs go.

The miscues were reminiscent of last season when both struggled at times as the Vikings' depleted secondary dealt with injuries and the trade of Benny Sapp to Miami in the preseason.

But Joe Woods, the Vikings defensive backs coach, said he has seen improvement from Allen and Cook this summer and doesn't think Saturday's performance necessarily reflects where they are in terms of progress. "I think the one thing from both of them that I see is confidence," Woods said. "Their confidence is growing, and the only way they are going to keep developing that is through playing."

Allen and Cook are going to be given every chance to win important jobs in the secondary. If they don't grab the opportunity, and if the Vikings don't sign a free agent or make a trade, then guys such as fifth-round pick Brandon Burton, undrafted free agent Devon Torrence and former Gopher Marcus Sherels are going to get a shot.

The immediate opening is for the nickel job, and Cook appears to be the leading candidate to win a spot that would put him at the left corner on passing downs with Antoine Winfield moving inside. Winfield and Cedric Griffin are the starters, but Griffin has torn the anterior cruciate ligament in both knees the past two years, and a close eye will be kept on him.

Cook likely would have been the first choice to take over at right corner last season when Griffin tore his right ACL in an October loss at New York. He had an excellent rookie training camp but ended up suffering meniscus tears in both knees at different points and had to have arthroscopic surgery each time.

Cook started five of the six games in which he appeared and ended the season on injured reserve. He was benched twice and attempted to return too quickly in late October when he struggled in a loss at Green Bay.

"I definitely feel 10 times more mentally prepared than I did last year," said Cook, who has fully recovered from the procedures on his knees and also has lost about 10 pounds from his 6-2 frame. "[The coaches have] even given me compliments about my maturity level going up and my willingness to learn the game and willingness to take coaching. They've commented about it a lot, and I definitely feel like I've changed as a person and just grown up more."

The 5-9 Allen, a third-round pick in 2009, started 11 of the 14 games he played in and had two interceptions. But his tackling left something to be desired.

"I learned so much being able just to play [last season]," Allen said. "The best way to learn is being in the game, and I think last year when Ced went out and being able to start it was something that was tremendous for me. You can practice and look at your playbook, but when you're going against the best of the best every week, that's the best experience. So I think I learned a whole lot from that."

What's important is whether that experience will pay off. Woods mentioned that with all the multiple-receiver sets in the NFL, the Vikings could go to more dime looks (six defensive backs). That could mean both Allen and Cook joining Griffin and Winfield in certain situations.

But if that's going to happen, the mistakes the Vikings saw Saturday are going to have to be cleaned up.

"They understand the situation," coach Leslie Frazier said. "They know it's a golden opportunity for our guys in the secondary to step up. They see it as well as we do, as well as you do, and so they'll get another opportunity this coming weekend and throughout this preseason, and hopefully somebody will step up, because we really need it to happen."