Who is that masked man?

As impossible as it might be considering his shoulder-length blond locks that nearly conceal the nameplate on his No. 20 jersey, as a backup, Craig Steltz seeks anonymity when he steps onto the football field.

If he isn't noticed, he considers that good.

Never mind that the rookie had to man free safety the entire second half Sunday - with the Bears trailing winless Detroit no less - after Mike Brown suffered a calf injury.

"You want to practice (during the week) like a starter so the front seven doesn't even turn around and know there's a change," Steltz said.

"That's how you want it to happen."

It didn't.

Steltz wasn't stealth.

He got noticed by making one of the game's biggest plays in the Bears' 27-23 win.

The Lions were looking to add to their 23-20 lead early in the fourth quarter when Steltz intercepted a Dan Orlovsky spiral at the goal line. The pass nearly reached the hands of 6-foot-5 star Calvin Johnson, but Steltz snared it and returned the pick down the sideline before being pushed out of bounds at the Bears' 43.

"We needed to make a big play," said the 6-1, 210-pound Steltz, who joined Kevin Payne, Corey Graham, Trumaine McBride and Zack Bowman as other Bears to record their first NFL interception this season. "As a defense, we had to hold them."

"It was an excellent play by Craig Steltz," said defensive coordinator Bob Babich, smiling like a proud dad. "To have a guy like that step up is a big deal."

Steltz, a fourth-round pick out of Louisiana State, had little time to think about being thrust into the starting lineup, replacing the well-respected Brown, who earlier in the game snagged his 16th career interception.

"It was kind of a second-half thing," Steltz said. "They said, 'Hey, Mike's down. You're in.' I said, 'All right.' You really don't have time to get butterflies in your stomach. You just go out there and play."

Steltz was credited with 2 tackles and a defended pass, as well.

"It just shows you our team depth," cornerback Nathan Vasher said. "Craig Steltz did an excellent job when Mike went down. Coming in and stepping up and making plays, when you have young guys doing that, it helps make us a better team."

The Bears played better defensively in the second half. They shut out Detroit after allowing Orlovsky, a career backup who's playing in place of the injured Jon Kitna, to throw 2 touchdown passes and put up a 113 passer rating in the first half.

"That's how we're supposed to play," head coach Lovie Smith said. "The first half, we can't allow them to catch some of the passes that they did. We're better than that. The second half, that's what you should see from the Chicago Bear defense."

With the Bears leading by the eventual final score and less than three minutes to play, a 12-yard punt by Brad Maynard gave the ball to Detroit at its own 42. But Lance Briggs forced a fumble after a catch by tight end Michael Gaines and recovered the ball.

"That's what wins ballgames ­- turnovers," Steltz said. "Anytime we can get the ball back to our offense, we can win games."