GREEN BAY—A rite of passage in Week 1 football is reacting to the element of surprise.

Teams have had the entire offseason and preseason to tweak their schemes and draw up plays their opponents haven't seen. Mike McCarthy has said many times that 20 to 30 percent of the snaps in a Week 1 game are what he refers to as "unscouted looks."

By all indications, McCarthy and his staff have gained a decent edge over the years in that department. After a shutout loss in McCarthy's first game as head coach in 2006, the Packers won five straight season openers.

But the Packers might have met their match last year, and they got a double dose of unscouted looks from the offense of the San Francisco 49ers.

In the opener, the 49ers came out scripted and sharp, putting the Packers on their heels as quarterback Alex Smith directed four straight scoring drives in the first half (one TD, three FGs). Only a Clay Matthews third-down sack on the opening drive of the game stopped San Francisco from going 5-for-5 out of the gate, but the 16-7 halftime hole was still too deep for Green Bay in a 30-22 defeat.

Then in the NFC divisional playoff, with the 49ers having switched to QB Colin Kaepernick at midseason, San Francisco used a first-round playoff bye – a reprieve the Packers surrendered on a last-second field goal in Minnesota in Week 17 – to make the read option a much larger focal point offensively than it had been. The Packers weren't prepared, and it showed in the 45-31 decision.

Now it's Week 1 again, and the 49ers have had another offseason to expand their playbook heading into Sunday's rematch at Candlestick Park. McCarthy's estimate of 20 to 30 percent might not cover it.

"Creativity schematically is something all teams do in the offseason," McCarthy said. "With regards to the 49ers, you can see in the preseason video, they didn't really show a whole lot. There will be some new looks. I think that will definitely be part of their offensive approach."

Count on it. The Packers have been forced to deal with the read option since January, but there's no guarantee the 49ers will run it as much as they did in the playoffs. Or perhaps they've added even more "options" for Kaepernick out of read-option looks. They only ran it extensively in three postseason games. It could go either way.

As it is, Kaepernick has only 10 NFL starts total, so from a scheme-creativity standpoint, San Francisco Head Coach Jim Harbaugh is in basically the same place in his third year at the helm as he was heading into 2012 with Smith under center.

"It was the guy's second year in the league," cornerback Tramon Williams said of Harbaugh, referring to last year. "Coaches tend to grow within that time, and their players grow into that system also. They tend to add more things, add more concepts, and you know it's going to happen, but you don't know what it's going to be.

"When you see something, you have to adjust to it and maybe you see it later on in the game, and you have to pick up on tendencies like that."

Easier said than done in the heat of battle, but as safety Morgan Burnett said, "That's just part of the NFL." It cuts both ways, too.

"We don't know exactly what they're going to do, and hopefully we have some stuff they don't know we're going to do," defensive lineman B.J. Raji said.

"Week 1 is a peculiar week."

Speaking of peculiar, here's a rarity: The Packers haven't seen their season end with a postseason loss and then had to face that same team in the next year's opener in 71 years.

In 1941, the Chicago Bears beat the Packers in the Western Division playoff, 33-14. The rematch in the '42 opener was also taken by the Bears, 44-28.

That ancient history will be irrelevant come Sunday, but last year's double dose of unscouted looks from the 49ers won't be. The Packers will have to regain their Week 1 edge, and they certainly plan to. They've spoken all week that they believe they can turn the tide back their way.

"It doesn't matter what I think, it's how I play, how we play," Raji said. "I believe we'll play better. That'll be the difference."

For a look at the rest of the week's Packers-49ers headlines, click here.