Fox’s American Idol returned last week as a

Fox’s American Idol returned last week as a ratings juggernaut with its double dose of two-hour shows averaging a whopping 15.6 18-49 demo rating. The network also enjoyed a solid performance from serialized drama 24 with two, two-hour episodes that averaged a 5.8 18-49 rating, enabling Fox to pull within 0.2 of a rating point for the season 18-49 demo lead.

Clearly, what Preston Beckman, Fox evp of strategic planning and scheduling, described two months ago as the network’s “flailing cycle” has come to an end, with the network now poised to compete head-to-head with the other Big Three networks for the advertiser-friendly 18-49 demo crown.

Since Fox’s ratings low point last November, Nielsen Media Research data shows the network has increased its 18-49 demo ratings 17 percent to a 3.4, and now closely trails ABC, CBS and NBC, which, through last Wednesday, when the second Idol episode aired, were all averaging a 3.6 in the 18-49 demo for the season.

All three, however, are expecting boosts when Heroes (NBC), Lost (ABC) and Jericho (CBS) return with fresh episodes in the coming weeks. CBS will also get a huge bump when it airs the Super Bowl on Feb. 4. Still, with more than 70 hours of Idol and 20 hours of 24 left to run, as well as the continuing strong performance of drama House, Fox is poised to become the 18-49 frontrunner by the end of the first quarter.

But media agency execs said despite Idol’s blockbuster opening, the rival nets shouldn’t fold their tents just yet.

“There is room to do decently opposite Idol, but it has to be the right type of show,” said Steve Sternberg, evp of audience analysis at Magna Global USA. “CBS procedural dramas appeal to a largely different audience from Idol.” Sternberg also noted that two-thirds of the under-50 audience are watching something else in the time period.

“The other networks have to dig into Nielsen data, find out who is not watching Idol, and program toward those people,” echoed Brad Adgate, svp, director of research at Horizon Media.