GREEN BAY—Back in Week 1, all sorts of red flags flew the first time the Packers defense tried to match up with the 49ers offense.
A coverage bust left receiver Randy Moss all alone for a 14-yard touchdown pass, tight end Vernon Davis was seen running free for a 29-yard reception, and running back Frank Gore turned the corner late for an all-too-easy 23-yard TD run.
San Francisco was sharp and efficient in compiling 377 total yards. Quarterback Alex Smith was calm and comfortable, completing 20 of 26 passes on his way to a 125.6 passer rating.
Outside observers were questioning whether the Packers were in for another long year on defense, whether anything or anyone was going to prevent a repeat of the never-ending hemorrhage of yardage and big plays from 2011.
Immediately after the game, a 30-22 Packers loss, the players insisted the defense would get better, that it wouldn't be the same story from the prior year, and they were right. The Packers finished the regular season ranked 11th in both yards allowed and points allowed, impressive improvements from the year before.
So, what changed? Mainly two things – communication and experience, and they went hand in hand.
"Every rep you get together as a team, the communication errors go down, and the missed assignments," linebacker A.J. Hawk said. "Our defense is very keyed on communication between each other, and if you're not all on the same page, bad things can happen."
In part, that's what led to Week 1 looking an awful lot like the previous season, with big plays gashing the defense. But the communication steadily improved.
Players who received a call or check on the field began relaying it back to the source, to emphasize they heard and understood it. That's not always possible in the fast-paced heat of battle, but when time allowed, it became the procedure.
"Everyone knows what's going on out there, everyone's understanding the defense," cornerback Tramon Williams said. "It's a whole lot better than it was. We put a lot of focus on it."
The Packers also emphasized bringing along all the young defenders they threw into the fire early. The first two draft picks, Nick Perry and Jerel Worthy, would eventually get hurt, and they're not around for the playoffs.
But cornerback Casey Hayward grew into a playmaker, outside linebacker Dezman Moses added to the pass rush, defensive lineman Mike Daniels found a role in the sub packages, and safeties M.D. Jennings and Jerron McMillian became steady presences in the back end.
"We've grown a bunch since that first game," Hawk said. "We've definitely taken some big steps since Week 1, but so have they."
Indeed, the 49ers' biggest change is the mobile and athletic Colin Kaepernick in place of the pocket passer, Smith. Kaepernick adds a running threat when the play breaks down and with a package of zone-read option calls involving running back Frank Gore.
Being assignment-sound against Kaepernick and his zone-read looks is critical.
"You can't get nosy," safety Morgan Burnett said. "You have to do your responsibility. If you have the running back, you have to stay on the running back. If you have the quarterback, you have to stay on the quarterback. Because if you get to guessing and just running around, they can make you pay for it."
The 49ers also like to exploit mismatches with their two tight ends, Davis and Delanie Walker. Against the Packers in Week 1, Walker didn't catch a pass, but since Kaepernick took over at QB in Week 11, Walker has 14 of his 21 receptions, 255 of his 344 yards and two of his three TDs.
"Those guys are not like your normal tight ends," Burnett said. "They can split them out, and you really have to treat them like wide receivers, because they have speed like wide receivers. They're a big factor in their offense."
They are factors among the many the Packers must account for in this playoff showdown, but compared to Week 1, they're all the more prepared to do so.
"They can cause some problems for you," Hawk said. "But that's why we're here. That's why there's only eight (teams) left."