Defensive tackle Dan Williams closes in on 49ers quarterback Colin Kaepernick during last year's meeting between the Cards and Niners in Arizona.

One of the Cardinals' main objectives on Sunday against the 49ers will be to pressure the quarterback. The defense has only two sacks through the first two games, and it's been a struggle to get heat without the aid of a blitz.

This game will present another wrinkle, as the Cardinals face their first mobile signal-caller of the season in Colin Kaepernick. He had nine carries for 66 yards last week and finished 2013 with the fourth-most yards on the ground (521) among quarterbacks.

With pocket passers, it's easy for rushers to pin their ears back and get in the backfield any way they can. When a player like

Kaepernick has the ball, he can take off if a defensive end pushes too far up the field.

"He's a tall, fast, rangy guy," defensive end Kareem Martin said. "Watching film, I've seen where guys collapse the pocket and even get a hand on him, but he still finds a way to escape. When you have a guy like that, you have to rush as a team. Everybody has to be where they're supposed to be, so if he's flushed you're where you need to be."

Kaepernick threw 12 touchdowns and 10 interceptions within the pocket in 2013, compared to 12 touchdown passes and only one interception outside it. It's a fine line, as the defense wants to keep Kaepernick in the pocket but doesn't want him feeling comfortable enough to read through multiple progressions.

"There's definitely a major catch-22 there, because you talk about staying in lanes and controlling the pocket, things of that nature, but if you do it too controlled you end up locked up with the lineman who has control of you," linebacker Thomas Keiser said. "And even if the lanes do look pretty good, if he still wants to escape, he may be able to get you if the lineman's got a hold of you. The biggest thing when you're rushing someone whose as talented running as he is, you can't rush scared. You still have to get after him and cover each other. It's definitely not an easy task, by any means."

AN ELLINGTON TO MIMIC THE OTHER

The 49ers have found a stand-in to emulate the moves of Cardinals running back Andre Ellington during practice this week. His cousin Bruce, a fourth-round pick in May, is taking snaps at scout-team running back as the two teams prepare to face off.

Andre said Bruce is a pretty good doppelganger, but it's not quite the real thing.

"I told him they'll never get the best look until Sunday," Andre said.

The Ellingtons faced off twice in college when Andre was at Clemson and Bruce at South Carolina, and the Gamecocks emerged victorious in both matchups.

"We were rivals in our childhood, too," Andre said. "We were always competing. Whether it was a pickup game or something, he was always on the opposite team. I'm always going against him. I thought it was pretty interesting that he was drafted to San Fran, to keep that rivalry going.

"He's up 2-0, but I told him it's over now. I'm taking back the winning streak."

The 49ers and Cardinals face off twice a year, and the Ellington family plans on making it a reunion in each location. Andre's mom, Bruce's parents, an uncle and several cousins will be in town this weekend.

HOUSLER, ZASTUDIL DO NOT PRACTICE

Tight end Rob Housler (hip) missed practice Thursday after not showing up on the injury report the day before. Punter Dave Zastudil (groin) did not practice after being limited Wednesday.

Zastudil missed the first two games of the season, although the Cardinals cut fill-in punter Drew Butler on Tuesday. Linebacker John Abraham (concussion), linebacker Alex Okafor (thigh) and defensive end Frostee Rucker (calf) also didn't practice.

Quarterback Carson Palmer (shoulder) was limited, as his status for Sunday remains cloudy. Running back Andre Ellington (foot) was upgraded to limited after missing practice on Wednesday and linebacker Larry Foote (shoulder) was also limited.

For the 49ers, cornerback Tramaine Brock (toe), tackle Anthony Davis (hamstring), tight end Vernon Davis (ankle/knee), center Marcus Martin (knee) and tight end Vance McDonald (knee) did not practice.

Tackle Joe Staley (knee) was upgraded from limited to full practice, while Kaepernick joined the injury report with a back injury but practiced in full.

CARDINALS SELL OUT 49ERS GAME

The Cardinals announced another sellout for Sunday, their 87th straight at University of Phoenix Stadium. The game will be broadcast on FOX 10.