I hate previewing the first couple games of the new NFL season. It's all speculation when neither team has played any (or enough) regular season games to predict what's going to happen next. Obviously I could look at last season but how a team was playing 12 months ago isn't nearly as accurate as how they played last week. And the preseason is useless.
Will the Packers stop the 49ers' offense?
Unfortunately the Packers are poorly built to stop the run. They rarely play more than three defensive lineman and spend as much time in their nickel package as any defense in the league. On the other hand, the 49ers are built to run the ball and they're very good at even when they're not playing against the Packers. Football Outsiders ranked them No. 3 overall last season on the ground.
QB Colin Kaepernick set a rushing record for a quarterback against them in the Packers' playoff loss, and RB Frank Gore was no slouch with a 5.2 ypc average in that game. The Packers' defense can't stop them from running but they have to stop the carries of more than 20 yards. Make them work the length of the field.
The 49ers' passing game should be less this season without WR Michael Crabtree, but WR Anquan Boldin is a decent replacement and the Packers were still gashed last January by two 40+ yard passes Gore and TE Vernon Davis. That was unusual, the Packers weren't prone to giving up big pass plays, but they have to fix whatever problems they had before. I'm not expecting Kaepernick to have another record setting game, but I'm not expecting a shut-down defensive effort either. This might be another shoot out.
Will the 49ers defense stop the Packers' offense?
The 49ers defense is very good, No. 2 overall according to Football Outsiders last season, but the Packers' offense almost kept up with the 49ers' offense in their playoff game. With five minutes left in the third period, the Packers missed on a 3rd down conversion at mid-field and were forced to punt. At that point, it went from a shoot out to a blow out.
Their one big addition, who might turn this game around, is RB Eddie Lacy. I haven't seen enough from him this preseason to expect he'll be the next great franchise RB, but the Packers were killed in time of possession (21:59 to 38:01) in their last meeting and the offense has to find a way to stay on the field. They need to give the defense a break. A strong running game that can eat up the clock and take away drives from the 49ers will help the defense.
For the Packers to win, they're going to have to score a lot of points and get more from their defense. It's possible; the Packers are as healthy now as they're going to be all season, with CB Casey Hayward as the only player who's not on I.R. but expected to miss the game. If the Packers do win, it'll be because they did to the 49ers what the 49ers did to them last January in the playoffs, and win a shoot out.