Green Bay and Houston are two of the more surprising of the NFL’s early undefeated teams, and both teams are winning with young defensive talent. The Packers combine young players such as linebacker A.J. Hawk and safety Atari Bigby with talented players just entering their primes, such as linebacker Nick Barnett and defensive end Aaron Kampman. The Texans are building around four young stars chosen early in recent drafts: cornerback Dunta Robinson, linebacker DeMeco Ryans, defensive tackle Amobi Okoye, and last year’s first overall pick, defensive end Mario Williams.

This week, these two young defenses will face their toughest challenge of the season as they face the teams that had the two best offenses in the league a year ago.

CHARGERS (1-1) at PACKERS (2-0)
Sunday, 1 p.m.

The Chargers went into New England last week looking to avenge a January playoff loss. They left in shame after being thoroughly dominated for 60 minutes in a 38–14 loss that wasn’t even as close as the score looked. Now San Diego fans wonder: How far has this team fallen from the heights of last year’s 14–2 season? The biggest concern in San Diego is reigning MVP LaDainian Tomlinson, who has been kept to just 68 rushing yards in 35 carries over the first two games — less than two yards per carry. So far, this concern is a bit misplaced. Chicago and New England feature two of the strongest run defenses in the NFL, and Tomlinson is not immune to the power of schedule strength. He certainly wasn’t going to get any carries late in last week’s game, not with San Diego trying to make up a 24-point deficit.

Tomlinson is far from the first NFL great to endure early struggles. After two games in 1997, Barry Sanders had just 25 carries for 53 yards. Over the next 14 games, he ran for 2,000 yards.

The Packers came into the season with a young, maturing defense, and their 2–0 start is less of a surprise than people think. Nonetheless, that defense is built around stopping the pass, not the run. If Giants backup Derrick Ward can gain six yards per carry against the Packers, Tomlinson really shouldn’t have trouble breaking out of his slump.

The other important part of the Chargers’ offense is tight end Antonio Gates, and he hasn’t had any problems so far. This is the final game in a three-week stretch where San Diego has played the three defenses which did the best job of stopping opposing tight ends last year. Gates gained 107 yards with a touchdown against Chicago, which ranked first in 2006, and then 77 yards and a touchdown against New England, which ranked third in 2006. The Packers ranked second in 2006, and they won’t stop Gates either. Green Bay can win if quarterback Brett Favre can take advantage of the weak San Diego secondary. It won’t be easy if two of his top three receivers, James Jones and Greg Jennings, miss the game with hamstring injuries. As for the ground game, Green Bay’s inexperienced running backs will need to deal with stout Chargers nose tackle Jamal Williams, who should be healthy enough to play after a hyper-extended elbow took him out in the middle of last week’s loss.

On paper, San Diego is still the superior team, but they’ll be playing on the road at a packed Lambeau Field. If San Diego loses a close game, fans will start to panic, but a close road loss to a good out-of-conference opponent is probably the least worrying loss an NFL team can have.

If Green Bay blows out San Diego the way New England did, however, panic in San Diego is probably the correct response.

COLTS (2–0) at TEXANS (2–0)
Sunday, 1 p.m.

What might have been an intriguing match-up is somewhat ruined by a knee injury to Houston wide receiver Andre Johnson, who is expected to be out for roughly a month. The third overall pick in the 2003 draft, Johnson is so far superior to the other Texans’ receivers that he has become virtually the team’s entire offense. So far this year, quarterback Matt Schaub has thrown more passes to Johnson (20) than to all the team’s other wide receivers and tight ends combined (17).

Conventional wisdom says the Colts struggle against division opponents, but last year’s 27–24 upset was actually the first Houston win over Indianapolis in franchise history. They won the game by running the ball over and over against the historically poor Colts run defense, a season-high 42 carries for 191 yards. This year, the Colts will stack the box to stop Houston’s running game and dare Schaub to beat them by throwing to all those non-Johnson receivers he’s been ignoring so far.

Meanwhile, while the Houston defense has been impressive early, consider the quarterbacks they have faced. Chiefs fans argue about whether Damon Huard should start over Brodie Croyle. Panthers fans argue about whether Jake Delhomme should start over David Carr. Colts fans argue about whether Peyton Manning should start over Johnny Unitas on a theoretical team featuring the greatest quarterbacks of alltime. That should illustrate the difference between Houston’s first two opponents and the team they play this Sunday.

Mr. Schatz is the editor in chief of FootballOutsiders.com.