(Eds: With AP Photos.)

By JANIE McCAULEY

AP Sports Writer

SANTA CLARA, Calif. (AP) - NaVorro Bowman is no longer just San Francisco's other inside linebacker, or the inexperienced young guy. Teamed with Patrick Willis, he gives the 49ers one of the most feared linebacking tandems in the NFL.

Opposing offenses that try to focus Willis find they must also reckon with Bowman. The second-year pro out of Penn State has made huge strides for an attacking defense that is tops in the league at stopping the run and hasn't given up a rushing touchdown this season.

Bowman's rise as a replacement for the departed Takeo Spikes has meant so much for the playoff-bound 49ers (10-3). They've also gone 35 straight games without allowing a 100-yard rusher. Bowman's team-leading 113 tackles are a significant jump from his 46 in 2010.

He loves working alongside Willis as part of one of football's best duos.

It is a huge accomplishment, a huge title that we can run with, but we don't feed into those things,'' Bowman said.We just play our game out there, play within the scheme and make plays that are our plays to make. Me and Pat, we think of ourselves as one of the best and we have to keep going out there and proving it every single Sunday.''

Even with Willis nursing a right hamstring injury that kept him out of last Sunday's 21-19 loss at Arizona, Bowman causes problems for other teams by himself. The Steelers (10-3) know Bowman will bring it every snap Monday night at Candlestick Park regardless of whether Willis has returned.

Obviously, he's a special player,'' Pittsburgh running back Rashard Mendenhall said of Willis,but they have a guy in Bowman who's playing well.''

The 49ers are the first team since the 1920 Decatur Staleys to not allow a rushing touchdown in the first 13 games of the season - and if San Francisco does it once more, the team would become the first in NFL history to go the first 14 games without giving up a TD on the ground.

Bowman and his unit take pride in that even if it's never discussed. The 49ers' third-round draft pick last year showed signs of the impact player he has become while starring on special teams as a rookie. His 20 special-teams tackles ranked third in the NFL last year.

They kind of knew what they had in him last year and then this year he came in, starting with Takeo being gone, and he kind of exceeded everybody's expectations,'' 49ers defensive end Justin Smith said Thursday.He stepped it up. Not only is he playing well, he knows his stuff, inside and out, on the defense. He's a leader out there, too. He's the total package in year two. Having him and Pat in there is unbelievable. I don't know who'd be better.''

Football has long been Bowman's outlet after growing up in a crime-stricken area of Washington, D.C. While he doesn't make goals based on numbers, Bowman realizes his improved play has been a big part of the 49ers getting back to the playoffs after an eight-year absence.

There's not really a limit I have with the expectations,'' Bowman said.I'm on track. I'm doing the things that I expected I could do. There are a lot more things I can do better at, and every single week I try to do that.''

Bowman looks back fondly at the guidance he received from Hall of Fame linebacker Mike Singletary, who was fired as San Francisco's head coach after a loss at St. Louis in the second-to-last week of 2010.

Bowman credits his development to that short time with Singletary.

He meant a lot,'' Bowman said.He was a hard-nosed coach and he stayed on my back. That's one of the things I carried to this year - just keep working. You're never good enough. The little things are really what matter. That's what he harped on every single day in practice in my first year as a rookie. He really benefited me.''

The main thing Bowman learned from Singletary was to lead by example.

Don't talk about it,'' he said.Don't walk around like you are (big time). Just set the example by your play and by your work ethic and by how you carry yourself.''

Bowman quietly goes about his business and lets others speak out on the team's resurgence this year under first-year coach Jim Harbaugh. He would rather save his energy for making key plays on the field.

And this defense works every down not to miss tackles or chances to change the game by forcing turnovers.

The way NaVorro's playing, just the pure production to be in there and making all those tackles - and doing it game-in, week-in, week-out - for a second-year guy, first year starting, obviously he's doing really well,'' quarterback Alex Smith said.I think we all understand that. He's playing at a really high level right now, and the guy works really hard. He's humble and obviously really talented.''

Just when many figured the 49ers were doomed when they lost Spikes after the lockout, Bowman has come up big time and again.

He's had a tremendous impact. Almost from the first day of camp until now, he's really played well for us,'' defensive coordinator Vic Fangio said.He's been an important player for us and I can't say enough good things about him. Now's the time though, where he's got to put the pedal to the metal and finish these last weeks with even better play.''

Notes: Willis wasn't in uniform for Thursday's practice and neither was LT Joe Staley, who has a head injury and hasn't been medically cleared for anything but walk-throughs.