Manning a stiff test for young 49ers secondary

Facing their toughest test of the young season, the San Francisco 49ers look to keep their three-game winning streak alive on the road against the ever-dangerous Peyton Manning and the high-octane Broncos offense.

The 49ers’ second-ranked passing defense will have their hands full trying to throttle the Broncos’ fourth-ranked passing offense coming off a 31-17 trouncing of the New York Jets in which Manning racked up three touchdowns and 237 passing yards.

With their preparation cut short by Monday Night Football, head coach Jim Harbaugh Wednesday acknowledged the grueling task of trying to contain Manning:

“Big challenge, huge task. Tremendous offense, great quarterback, capital G at the highest level. That competitive challenge is something I think our team, our defense, will be up for.

To compound matters more, LB Patrick Willis and nickel cornerback Jimmy Ward were absent from practice Wednesday after sustaining injuries during Monday night’s game.

Ward’s injury will increase the playing time of both Dontae Johnson and Chris Cook, but perhaps the biggest question mark for Harbaugh and the 49ers defense is LB Chris Borland, who will start in Willis’ absence.

Borland’s pugnacious approach on the field has earned praise from the coaches, but the rookie linebacker’s instinctual coverage has allowed him to be burned through the air by deceptive NFL quarterbacks.

Manning may look to take advantage of the overzealous Borland, though Harbaugh expressed his utmost faith in the 23-year old’s ability to step into his role:

“Chris, he’s shown that he can play. He’s shown it on special teams two weeks ago, four tackles. This past week he tackled well, broke up two passes. Excited for him.”

Both Borland and LB Michael Wilhoite may prove to be instrumental in stopping one of the the Broncos most explosive offensive weapons in tight end Julius Thomas.

Spanning back to last season, the Stockton-born Thomas has caught a team-leading 21 touchdown passes from Manning, making him a key target of the veteran quarterback in red zone situations.

Now in his 17th season, the elite Manning may have a field day with a young and inexperienced defensive group that could feature first-year starters CB Chris Culliver, LB’s Borland and Wilhoite, as well as rookie CB Johnson.

The strong play of safeties Eric Reid and Antoine Bethea, as well as the continued ascendence of CB Perrish Cox, could prove to be key factors while attempting to stem the tide of Manning’s offensive prowess.

After praising the 49ers defensive unit as a whole, Broncos head coach John Fox singled out Cox as a key contributor to San Francisco’s recent success:

“He’s the first guy that comes to mind because I know how good he is. I don’t know what ya’all’s familiarity with him was till recent but I know he’s a very very capable athlete and he’s played very well.”

The crafty Manning may not give Cox an opportunity to add on to his team-leading three interceptions, but the four-year veteran will be instrumental in keeping a talented WR core — featuring Emmanuel Sanders, Wes Welker and DeMaryius Thomas — from making big plays downfield.

Follow @SFBay and @ShawnWhelchel on Twitter and at SFBay.ca for full coverage of the San Francisco 49ers.