To pick one guy from each of the three levels of the Chicago Bears' defense (line, linebackers, secondary) as having the biggest potential impact in Sunday's game, the likely choices would be defensive tackle Tommie Harris, middle linebacker Brian Urlacher and safety Mike Brown.
It's probably most difficult to control the impact of Urlacher and Brown, because neither lines up at the line of scrimmage. They both have the freedom to roam the field, and they can't simply be blocked at the point of attack.
The one player the Packers can more directly focus on is Harris, but it will be no small task to limit him. Just because you can line someone up directly across from him doesn't mean he can be neutralized, because he's simply that good.
Throw in the fact that the two players who will be responsible for Harris most of the time Sunday will be rookies playing their first NFL game -- guards Tony Moll and Jason Spitz -- and you have what may be the key matchup the Packers must win, or at least hold their own, in order to have success against Chicago's renowned defense.
"He's quick and strong, and Tommie has an excellent pass rush move," said center Scott Wells, who started both games at left guard against the Bears last year. "He has a good motor so he's always moving around, he gets off blocks, it's hard to stay on him. You put those things together, it makes a good d-tackle."
The Bears' first-round draft pick in 2004 out of Oklahoma, Harris (6-3, 295) is in his third season and went to the Pro Bowl last year. Using his athleticism to shoot gaps makes him a disruptive force against both the run and the pass, and last year's three sacks and seven tackles for loss barely scratched the surface of his ability, according to his coach.
"Tommie's numbers haven't shown it so far, even though he went to the pro bowl last year," Bears coach Lovie Smith said. "He hasn't been a big sack guy. That's a part of his game I think will come along soon.
"I think he has outstanding talent at the position. Very few inside players have ability like Tommie Harris."
But don't expect either Moll or Spitz to be intimidated.
In meetings and film study, Wells has been sharing what he learned from last year, and the help they can expect from the center position in the blocking scheme, to help the rookies prepare for Harris.
"It's going to be a true challenge and a gauge to see where I'm at in my progress," Spitz said. "Like any other game you have to prepare the same way. You have to try to pick up the guy's tendencies and go from there."
Along with Spitz, Moll got a taste of some of the league's best in the preseason. Originally playing tackle, Moll blocked well against San Diego outside linebacker Shawne Merriman, earning him the promotion to starting guard. There, he faced defensive tackles Rod Coleman of Atlanta and Sam Adams from Cincinnati, two former Pro Bowlers.
"I've had some great looks from those guys, and he's right up there, a very good athlete," Moll said of Harris. "I'm approaching it the same way I've gone into all four of these games. I'm just trying to prepare as much as I can and be as physical as I can."
According to Wells, both rookies have improved "leaps and bounds" from the first preseason game, particularly with regards to pass protection.
But as any veteran knows, the preseason is left behind as the regular season arrives. Harris only makes that step up a little steeper.
"For Jason and Tony, I'm sure preseason was an eye-opener to them, but this is for real and whoever we're playing in the first game, it's going to be different," quarterback Brett Favre said. "It's going to be different than what you face in preseason. There's only one way to figure it out, and that's to play and take your medicine along the way. I'm sure they'll get beat at times, but I know they'll play with a lot of intensity and desire to win."