The two biggest games of NFL Week 4 each match up two of the seven remaining unbeaten teams. They will be played on the first day of October, but these games may have major implications for playoff seeding in January.

SAN DIEGO CHARGERS (2-0) AT BALTIMORE RAVENS (3-0)
(Sunday, 1 p.m.)

For the first two weeks of the season, these were the two most dominant teams in the NFL. San Diego won its first two games by a combined score of 67–7; Baltimore won its first two by a combined 55–6.

But it’s hard to get a handle on what those scores mean this early in the year. Not one of the teams that fell to San Diego or Baltimore has won a game against anyone else this year, either — including Cleveland, which very nearly upset the Ravens last week before a late interception gave Baltimore the chance to pull out a 15–14 victory.

Just like every year, the Ravens are driven by their defense, the best in the league so far. But their offense is still mediocre despite the headline addition of quarterback Steve McNair. Right now, the problem is that the Ravens can’t seem to put together a game where they are successful both on the ground and through the air. In Weeks 1 and 3, the Ravens averaged nearly six net yards per pass but only ran for 3.5 yards per carry. In Week 2, they gained five yards per carry but a dismal 3.6 net yards per pass.

For the Chargers, on the other hand, everything has hit on all cylinders. First-time starting quarterback Philip Rivers looks great. The offensive line has yet to allow a sack. LaDainian Tomlinson and Michael Turner are an awesome one-two punch on the ground.The front seven has been so ferocious rushing the passer that San Diego’s glaring weakness, its secondary, hasn’t even come into play.

To win this game, Baltimore has to attack that weakness. One reason to believe that they can: McNair is leaning heavily on no. 1 receiver Derrick Mason and tight end Todd Heap. And the only receivers to have any success against San Diego early on have been the opposing no. 1 receivers.Unfortunately for Baltimore, Heap is questionable with an ankle injury and may not play.

When Baltimore’s great defense meets San Diego’s powerful offense, the result is a draw. But unless McNair can withstand the Chargers’ pass rush to make big plays through the air, San Diego’s defense against Baltimore’s offense is assuredly not a draw, and this game won’t be either.

SEATTLE SEAHAWKS (3-0) AT CHICAGO BEARS (2-0)
(Sunday, 1 p.m.)

This could be a very early preview of the NFC Championship. Both Seattle and Chicago dominate their divisions with very little competition (except perhaps for Minnesota, which played Chicago close last week). Furthermore, the rotating division schedule that matches up the NFC West and NFC North means each team also gets to play the weak division foes of the other.

The trade for ex-Patriots wide receiver Deion Branch, combined with injuries to the top two tight ends, has effectively turned Seattle into an old school runand-shoot offense. In the second half of last week’s win over the Giants, the Seahawks used four wideouts on 16 of 37 second-half plays even though they led the game by at least three touchdowns during most of that period.

With 2005 league MVP Shaun Alexander out with a foot injury, the four-wide sets may be even more prevalent. But Maurice Morris isn’t necessarily a big step down from Alexander. In fact, on a per-play basis, Morris has been just as good as Alexander over the past three seasons according to Football Outsiders’ DVOA (Defense-adjusted Value Over Average) metrics.The main difference between the two running backs is Alexander’s durability — and after last year’s heavy workload, it’s clear that difference isn’t as big as it used to be.

Neither Morris nor Alexander has been able to get much going this year because of the departure of guard Steve Hutchinson, followed by a series of injuries on the offensive line.Against Chicago, the two starting guards will be Rob Sims, a rookie, and Chris Spencer, a second-year player whose main position is actually center. The Seahawks will also have to play backup Tom Ashworth at right tackle if starter Sean Locklear (questionable) can’t go. The stellar Chicago front seven should have a field day against these secondstringers, especially when they bring a blitz with the 2005 Defensive Player of the Year, Brian Urlacher.

The Bears do have a matchup problem with Seattle, however, because no linebacker in the NFL is better in pass coverage than Chicago’s Lance Briggs. When Seattle goes four-wide, Briggs has no tight end or fullback to cover. The Bears will have to cover Seattle’s slot receivers with nickel back Ricky Manning — who last year in Carolina was a big reason why the Panthers were horrible against the pass on third downs — or one of two rookies, free safety Danieal Manning and dime back Devin Hester.

When the Bears have the ball, opponents have been stacking the line to stop running back Thomas Jones, and he is averaging a miserable 3.0 yards per carry because of it. But it’s possible Seattle will be able to stop Jones without taking a safety out of pass coverage. Last year, Seattle ranked third in DVOA against the run, and the Seahawks are fourth so far this year.

When quarterback Rex Grossman has the ball, things get interesting, because so far both Chicago’s passing game and Seattle’s pass defense are improved over last year. The Bears are running well-designed plays that get their receivers open; in particular, they’re living off the deep in route when a safety is playing the run. But when he’s pressured, Grossman tends to run backward and throw wild passes instead of just taking a sack. The Seahawks bring a ton of pressure with just their front four and an occasional linebacker, and they led the NFL in sacks a year ago despite almost never blitzing defensive backs.

This should be the best game of the week: two great teams, evenly matched, both playing well in every phase of the game except running the ball — which means that no matter who takes the early lead, it will be hard to run out the clock and block the possibility of an exciting comeback.

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