SANTA CLARA, Calif. (AP) Four of the five positions on the San Francisco 49ers' offensive line are different than they were a year ago, and it's been a work in progress getting the group going.

The unit struggled in last week's 43-18 loss in Pittsburgh, allowing five sacks while the running game failed to replicate its performance from a season-opening win over the Vikings, when Carlos Hyde had 168 yards rushing and two touchdowns.

Now, the 49ers (1-1) head to Arizona to play the first-place Cardinals (2-0) hoping for a bounce-back performance from the offensive line.

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''After Week 1, I didn't believe anybody,'' coach Jim Tomsula said. ''A lot of people were sitting here talking about how great we were. And after Week 2, I don't really believe everybody on how bad we are. We're a work in progress, and we're on it.''

Left tackle Joe Staley is the only starter along the offensive line that's playing the same position he started last season. Alex Boone moved from right guard to left guard to replace Mike Iupati, who signed a five-year deal with Arizona in March.

At center, the 49ers are missing Daniel Kilgore, who is still recovering from a fractured lower leg suffered in last October's loss to Denver. He's on the physically unable to perform list, meaning he can't return until at least Week 7. Second-year player Marcus Martin is filling in for Kilgore.

Former Patriot Jordan Devey is the team's new right guard after being acquired in a trade Aug. 18 for tight end Asante Cleveland. The 49ers signed nine-year veteran Erik Pears in the spring to be a backup, but he's been starting at right tackle after former first-round pick Anthony Davis, 25, suddenly retired in June.

''It's an ongoing process. We're in Week 3 of the season,'' Staley said. ''I thought we did some good things, things that we improved on in Week 2. But, overall, not exactly where we want to be at all. Not a good effort last week, but I got 100 percent confidence in the group.''

The offensive line will have to deal with a Cardinals defense that's remained aggressive despite losing defensive coordinator Todd Bowles in the offseason - Bowles left to become coach of the New York Jets.

Arizona's new coordinator, James Bettcher, was on Bowles' staff coaching the outside linebackers and hasn't deviated from Bowles' attacking style.

''They still blitz. They still play hard. They're still going to be physical and those are things that we have to account for,'' 49ers quarterback Colin Kaepernick said.

The Cardinals defense was ranked in the top 10 in scoring the last two seasons, helping the team reach the playoffs in 2014.

''They bring a lot of exotic blitzes, and they take a lot of pride in their personnel groupings and the different kind of fronts they show,'' Staley said. ''Pretty similar to what they did in the past.''

NOTES: RB Reggie Bush is officially listed as doubtful for Sunday's game with a strained left calf suffered in the first quarter of Week 1. . WR Bruce Ellington (ankle) and TE Vance McDonald (knee) are both listed as questionable. Ellington did not play last week in Pittsburgh after sustaining the injury during practice. . The Cardinals announced Friday that WR J.J. Nelson (shoulder) is out, RB Andre Ellington (knee) is doubtful and G Mike Iupati (knee) is questionable. If Iupati plays, the former 49er will be making his debut with his new team.

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