The 49ers and Packers are two playoff teams from 2011 that shared a focus following their disappointing postseason exits – to upgrade one particular side of the ball.

The outcome of Sunday’s season-opening NFC showdown at Lambeau Field could come down to which team did the better job in that quest.

San Francisco’s defense ranked fourth in total yards in 2011, but its offense was 26th. Green Bay’s offense ranked third in total yards, but its defense was dead last.

As a result, the 49ers devoted most of their personnel upgrades to the offense, with the Packers doing the opposite.

The Niners’ first three draft picks were offensive players, though it’s debatable how much Illinois receiver A.J. Jenkins, Oregon running back LaMichael James and Wake Forest guard Joe Looney will contribute early.

More immediate impact is likely to be made by San Francisco’s free-agent signings. Added to the receiving corps are Mario Manningham, a Super Bowl hero for the Giants last year, and Randy Moss, who was lured out of a one-year retirement. Another Giants mainstay, running back Brandon Jacobs, was also brought on board to improve the ground game in short yardage and on the goal line.

The objective was to give quarterback Alex Smith more weapons, particularly in the passing game, which needed more threats than tight end Vernon Davis and receiver Michael Crabtree.

That said, the changes don’t have the Packers believing the 49ers have changed their offensive philosophy or team identity. They’re not expecting a wide-open air show. They’re planning for San Francisco to use its ground game, featuring Frank Gore, Kendall Hunter and Jacobs (if he plays; he’s dealing with a knee injury and is questionable) to control the clock and keep its hard-hitting defense fresh and able to attack.

“They were one of the best running teams in the league,” Packers defensive lineman Ryan Pickett said, referring to the Niners’ No. 8 ranking in rushing yards. “So we’re planning for them to come out and try to run. That’s the kind of ball they played last year, and that’s the kind of ball we’re getting ready for.”

Meanwhile, the Packers used their first six draft picks on defense to build their depth and give Defensive Coordinator Dom Capers more options for his various sub packages. Veteran defensive lineman Phillip Merling was added in free agency, too.

Several of the rookie draft picks could be playing significant roles from the get-go. Outside linebacker Nick Perry will start, defensive linemen Jerel Worthy and Mike Daniels appear pegged as inside rushers in the nickel, and safety Jerron McMillian got a lot of time as the dime back in training camp.

It’s asking a lot of rookies to play right away, but the Packers have little choice. No one is asking for a debut as sparkling as receiver Randall Cobb’s last year, when he caught  32-yard TD pass and returned a kickoff 108 yards for a score in the ’11 opener, but any performance half that good in the season’s early weeks could give the Packers a whole new feel for their defense.

“Just play ball,” Cobb said, when asked if he’s given this year’s rookies any advice about that first game. “We’ve been playing ball since we were little kids. Just go out there and have fun. Trust your training. That’s what we’ve been focusing on, doing what we’ve been taught to do, so when it comes to Sunday we just go out and play.”

The Packers will be looking to win their sixth consecutive season-opener. Mike McCarthy has won five in a row since getting blanked by Chicago in his first game as head coach back in 2006.

McCarthy’s teams of late have been known to start fast, and that bodes well, considering the schedule the Packers face in the first month. A short week precedes Thursday’s Chicago game, followed by a Monday night road contest at Seattle, and a home showdown with New Orleans.

Much was discussed in the media this past week, regarding the importance of a fast start, given the fact that a team’s fortunes can depend so much on momentum at the end. The bottom line is the finish matters more, of course, but a team may not get that chance to finish without a strong beginning.

“We’re at the starting line, and we learned a hard lesson, as hard as you possibly can,” McCarthy said. “We were the lead dog the whole year last year, but we didn’t finish.

“It’s a new season, lessons have been learned. Now we have the opportunity to apply them, and it starts Sunday.”