Fox has attracted more young adults than any other network for eight straight seasons, but may find it difficult to still be on cloud nine when the dust settles next May.

The Murdoch net, defined for the last decade by “American Idol,” saw the music competition series suffer a steep ratings decline earlier this year. And since “Idol” makes up more than one fifth of Fox’s second-half sked, the net’s overall averages tumbled too.

After holding off CBS in the adults 18-49 demo derby during the 2011-12 campaign, Fox won’t benefit as much as usual from sports in the upcoming season — and sports play an increasingly large role in determining season winners these days.

Fox won’t air the Super Bowl or a primetime NFL conference championship game (CBS has both), and in baseball, it gets the National League Championship Series (as opposed to the generally higher-rated American League counterpart).

First things first, though, Fox will try to fill some holes on its entertainment sked following the departure of “House” and the failure of last season’s high-profile rookie dramas “Alcatraz” and “Terra Nova.”

It’s adding just one new drama in the fall, Monday’s “The Mob Doctor.” Jordana Spiro is the show’s appealing lead, but it lacks a strong lead-in (“Bones”) and could get lost in a crowded 9 o’clock hour (though it will be the only Big Four drama airing then).

Instead, Fox’s fall focus will be in the comedy arena, where it expands its Tuesday block to four half-hours. “Raising Hope” and “New Girl” will serve as anchors, with sibling laffer “Ben & Kate” and Mindy Kaling’s young-doctor-in-the-city comedy “The Mindy Project” on the half-hours.

Both new shows exhibit promise, especially 8:30 p.m. entry “Ben,” and the lineup is well-skedded — even if “Hope” has yet to show that it’s strong enough to anchor a night.

“New Girl” faded in the second half of its rookie season, although it was an especially strong performer in DVR playback. Now that it’s paired alongside compatible comedies, perhaps more auds will tune in live.

Its primary Tuesday-night competition for younger viewers will be ABC comedy “Happy Endings,” which moves to the timeslot, though the Fox entry should win fairly easily in adults 18-34, and also draw more men.

Simon Cowell’s “The X Factor” will again be a big factor for Fox in the fall, occupying the same three hours weekly (two on Wednesday, one on Thursday) that “Idol” does later. The show underperformed in the eyes of most, but often won its timeslot, and teamed with “Idol” to make Fox’s Wednesday the top-rated night in 18-49 last season.

Fox has shifted “Glee” from Tuesday to the post-“X Factor” slot on Thursday, where in its fourth season it will compete for young women with ABC’s “Grey’s Anatomy” and NBC’s comedies. With cast changes and a new focus split between current high school students and graduates now living in New York, this is a key year for a show still looking for some of the magic it captured in its rookie season.

Friday, meanwhile, remains home to shows with limited ratings expectations (soph “Touch” and fifth-year “Fringe”), while Saturday will feature mostly sports this fall, with baseball and college football. Sunday’s animated laffer lineup is staying put, as the net would rather not try something new opposite NBC’s football.

Fox has a midseason ace up its sleeve in Kevin Bacon serial killer drama “The Following,” which should provide a “24”-like winter jolt on Monday. It will also bring men back to a net that has become increasingly female in recent years.

Bottom line: Fox should be a ratings force in the fall and pick up steam at midseason, but it might not be enough to catch CBS for the 18-49 crown.