The San Francisco 49ers might have the most formidable front seven in the NFL, but those aren't necessarily the guys leading the way for the NFL's top-ranked defense.

A team known for stopping the run is now even better at stopping the pass.

The 49ers led the NFL in rushing defense last season, but this year the pass defense ranks No. 1. A lot of that has to do with the play of four rangy defenders on the back end who have grown as a unit to become a shutdown secondary.

The next challenge comes Monday night in a key NFC West game against Arizona, a team with a weak running game that likely will have to throw to catch up with first-place San Francisco in the division.

That approach hasn't worked so well for opponents so far this season. In today's pass-happy NFL, San Francisco (5-2) has held five of its seven opponents below 200 yards passing and three to 115 yards or fewer.

Cornerbacks Carlos Rogers and Tarell Brown and safeties Dashon Goldson and Donte Whitner are in their second season together as a starting unit and seem to be getting better by the week. San Francisco has allowed an average of just 130.7 yards passing over its past four games.

"They're playing outstanding together," coach Jim Harbaugh said Saturday. "There's so much communication on the back end, communicating calls, communicating leverage, strength, formation, what the call is, technique they're going to play. There's a lot of communication that takes place back there."

The secondary was at its best during last week's 13-6 victory over the Seattle Seahawks, who did little damage through the air while finishing with 115 yards passing.

The 49ers frustrated rookie quarterback Russell Wilson into just nine completions in 23 attempts, and Goldson swooped in from the deep middle for his second interception to thwart a Seattle threat late in the third quarter.

Goldson, who like Rogers went to his first Pro Bowl last season, has picked up where he left off last year and the defensive backs around him also have shown growth.

"Dashon's just one of all the guys out there that has improved that much," defensive coordinator Vic Fangio said. "I'd say the same thing for Whitner, Brown, Rogers, (nickel cornerback Chris) Culliver, all those guys back there. When you get a bunch of guys improving a little bit, it adds up to big results."

It has led to a dynamic secondary that is benefiting from the strong play of a front seven that features All-Pro defensive tackle Justin Smith and All-Pro linebackers Patrick Willis and NaVorro Bowman.

Those players got a lot of attention last season when the 49ers ranked No. 1 in rushing defense, with several opponents abandoning the run altogether after falling behind. San Francisco's run defense remains strong but has slipped to 10th in this week's NFL rankings.

San Francisco's weekly defensive philosophy is to force teams to pass, which makes the secondary's performance even more impressive. There has been no weak link this year in a pass defense that finished higher than 20th in the NFL rankings just once over the past seven seasons. That was last year, when the 49ers were 16th.

"We're just more familiar and understand the defense better and we're comfortable in the system and playing it well right now," Brown said. "We're all on one page, and if we do give up a pass, it's nothing major. Everybody has opportunities to jump routes and make plays, and the good thing about it is guys are making those plays."

The 49ers will get tested in Arizona by a familiar face that has given San Francisco problems over the years.

Wide receiver Larry Fitzgerald has been a regular 49ers nemesis, and he played a big role in the Cardinals' 21-19 victory in Arizona last December — San Francisco's only NFC West loss during Harbaugh's two seasons with the team. Fitzgerald burned the 49ers for seven receptions and 149 yards receiving in that game, including a 46-yard touchdown reception that sparked Arizona's comeback from a 19-7 deficit.

The 49ers return to the scene of that loss Monday eager to show what their surging pass defense can do against Fitzgerald and the Cardinals.

"They move him around a lot so I think we'll all have an opportunity to go against Fitzgerald," Brown said. "We have confidence in all our guys that we all can cover and match up with those guys well."

NOTES: Harbaugh began his news conference Saturday by announcing that 49ers CEO Jed York and his wife Danielle have a newborn son named Jaxon, their first child. "The 49ers have more depth now and we're very excited about it, excited for them," Harbaugh said. "Good measurables and a strong name." ... OT Joe Staley, who did not practice earlier this week due to illness, was limited in practice Saturday and is listed as questionable to play against the Cardinals ... QB Alex Smith (sprained finger) and RB Frank Gore (bruised ribs) both are listed as probable ... The 49ers will be playing in their second consecutive prime-time night game against a NFC West foe after a Thursday game against Seattle on Oct. 18.