“American Idol” may be drawing its lowest ratings since 2004, but it’s already boosted Fox to its best competitive position in years.

Yesterday the network vaulted to No. 1 for the 2007-’08 season on the strength of this week’s two-night “Idol” debut, marking the earliest point in the last three seasons that Fox has pushed into first. The network finished No. 1 all three of those years.

That speaks both to the growing strength of the rest of Fox’s schedule and the general weakness of the broadcast networks this year. Fox is averaging a 3.4 adults 18-49 Nielsen rating, a tenth of a point ahead of the Big Three, which are all tied for second at a 3.3.

Fox is the only network to see year-to-year increases, up 3 percent over last year’s 3.3. It was also the only network to see substantial growth last fall, when improved performances for the dramas “House” and “Bones,” combined with solid ratings for new show “Hell’s Kitchen” and Thursday’s reality lineup helped guard against the network’s usual fall slump.

Fox also had its highest-rated World Series in three years, plus fewer disruptions for postseason baseball, the first round of which moved to cable.

But Fox’s leapfrog to No. 1 never would have happened if the other networks weren’t seeing declines from last year. NBC and CBS are both down 8 percent among 18-49s, from a 3.6 at this point last year, while ABC has slipped 13 percent.

A small portion of those decreases can be pegged to the writers’ strike, which has forced the networks to air more reruns and midseason replacements than usual, but a good portion is also due to the increase in the percent of Nielsen DVR homes, which has doubled since last year to 22 percent.

Season-to-date ratings above include only live and same-day DVR playback. When looking at seven-day DVR playback, the networks see substantial bumps in their ratings.

Still, Fox seems likely to surge even further ahead in the coming weeks. It has the NFC Championship game this Sunday night, which could score a double-digit 18-49 rating after the NFL divisional round drew its best ratings in 12 years. The network also has the Feb. 3 Super Bowl.

New show “Terminator: The Sarah Connor Chronicles,” though slipping after a big debut, still showed huge improvements over Fox’s season-to-date timeslot average on Mondays at 9 p.m.

And of course there is “Idol.” The show drew its smallest opening-night audience in four years, but it was so far out ahead of the competition that it almost didn’t matter. The first two episodes of the smash singing show have averaged a 13.2 rating, making them the year’s two highest-rated non-sports shows on broadcast, 48 percent better than the No. 3 show, the Sept. 27 premiere of ABC’s “Grey’s Anatomy” at an 8.9.

Even if “Idol’s” numbers fall off a bit more, it will still power Fox to an easy No. 1 this season unless one of the other networks’ reality shows really takes off, which seems unlikely.