Dre' Bly joined the San Francisco 49ers to fill some serious shoes.

The Niners secondary took a big blow before training camp when it lost veteran Walt Harris for the season as he recovers from knee surgery, which put the former Pro Bowl player's career in jeopardy.

Yet suddenly, the secondary is setting up to be one of the bright spots for an experienced defense that's on the rise. Coach Mike Singletary has plenty of capable choices on the depth chart, and the competition for starting spots may go down to the wire at right cornerback before the team opens the season Sept. 13 at Arizona.

Bly is the front-runner to win the job at that position over third-year pro Tarell Brown.

During training camp, the 49ers defensive backs displayed a ball-hawking mentality and the ability to make plays and jump in the passing lanes to deflect the football. That's something San Francisco desperately missed last season, when the 49ers managed only 12 interceptions. Seven of those came from the secondary _ three by Harris and two each by Nate Clements and Brown.

With Harris out, there's some work to do to make up for his production.

"When he went down, that left a void," Bly said. "That's when I got signed. He'll be tremendously missed. They say he was a great leader, a great veteran guy, had a great locker room presence. That's a great opportunity for me to come and be who I've been my whole life. I feel I can help because I'm a competitor, I compete.

"With Nate and the other guys we have, Tarell Brown, we can raise the level of play and do great things."

Harris tore a ligament in his knee during minicamp workouts on May 19 in a collision with receiver Dominique Zeigler, then underwent surgery later in the month. San Francisco signed Bly just one day after Harris' injury, clearly indicating Harris had no shot of playing this year.

Brown has been a standout on special teams in his first two seasons while also playing at nickel back. He believes the secondary will be a strength no matter who's on the field.

"I think we're going to be a dominant group," Brown said. "We have a lot of athletes back there, we have a lot of great veterans who have played in a lot of big games. And for us, we just have to stay with the little things, the attention to detail. Our coaches always stay on top of us about that, and bringing that swagger to the defense."

Bly, an 11th-year veteran and two-time Pro Bowler, faced his share of criticism last season with the Broncos. He made two interceptions, matching the lowest total of his career_ the first time he was in his fourth NFL season with St. Louis.

No question Bly is ready for a fresh start. He's as confident as ever at age 32.

"Just coming here, it has me hungry again," he said. "I haven't been hungry like this in a while. Based on how things ended last year in Denver, the critics were out there, saying I'm aging, saying I'm not an elite guy anymore, this and that. I've been healthy the last three years. I know I'm 32 but I haven't lost any of my quickness. I'm smarter and I definitely haven't lost any of my ball skills.

"To make the plays I've made since I've playing competitive ball, you just don't lose that. I haven't lost that. You've just got to be in the right situation. I'm in a great situation, a great scheme and I'm glad to be here."

San Francisco finished 13th in the league in total defense last season _ matching its highest spot in more than a decade _ with the secondary playing a key role in that. The 49ers led the NFL in total defense in 1997.

Defensive coordinator Greg Manusky joked that he'd love to keep 20 defensive backs if he could, though the number will probably be at least half that when the roster is trimmed to 53 players Saturday.

"It is a very solid group on the back end," Manusky said. "Even though we have a couple of young guys playing in the back, it seems like a veteran group, which is good. There are some young guys and some older guys all sprinkled in there. A very strong group of personalities and they want to be good and they want to show that they belong where they belong."

San Francisco, which plays its last exhibition game Friday at San Diego, has spent a lot of money to boost the secondary, too.

When the 49ers signed Clements to an $80 million, eight-year deal in 2007 _ with $22 million guaranteed _ it was the richest contract ever for a defender at the time.

Star linebacker Patrick Willis isn't the least bit concerned about the defensive backs playing behind him.

"I have all the confidence in the world. I wouldn't want another secondary back there," Willis said. "I think knowing the guys back there, they're very experienced, been playing a while, been playing the game of football for a while and then we've been playing for a while. Especially playing in this defense now going on three years makes it even better. So, hopefully all of that will play into our favor."

NOTES: Singletary said Thursday he has a "very good idea" what the 53-man roster will look like. ... The starters will play a couple of series or about 10-12 plays Friday, including QB Shaun Hill starting. Backup Alex Smith (injured thumb on throwing hand) won't play and No. 3 Nate Davis will get significant action. ... Singletary is holding out his two offensive stars: RB Frank Gore and WR Isaac Bruce. ... Starting right tackle Adam Snyder and left guard David Baas, both coming off injuries, will start and could play a few more plays than the rest of the regular starters. ... Also out are WR Arnaz Battle (shoulder), OL Cody Wallace (viral meningitis), LB Ahmad Brooks (knee), S Michael Lewis (concussion), WR Brandon Jones (shoulder) and LB Jay Moore (groin).