The opening-night ratings for Fox’s “American Idol” offer a good news/bad news scenario for the net’s rivals: While the megahit show looks to have peaked, there’s likely little the competish can do to take advantage of it any time soon.

Tuesday’s two-hour “Idol” bow more than doubled what ABC, CBS and NBC put up opposite it and easily stands as the season’s No. 1 entertainment telecast. Still, it came in more than 10% below the previous year’s record-setting debut. The show’s softest start in four years marked the first time it’s failed to build upon the previous year’s preem score.

Amid a writers strike, however, it’s unlikely that the competish can step up and seize on any “Idol” vulnerability. The show’s strongest competitor on Tuesday, CBS drama “NCIS,” for example, exhausted its final original episode opposite the “Idol” debut and will now go to battle with repeats.

It’s too early to draw any conclusions from “Idol’s” premiere, but its performance figures to be under even more of a microscope this year. The show faded some down the stretch a year ago amid a less-than-stellar season for music talent, and its continued vitality is important for the broadcast biz.

“My only expectation this year was that it would be huge again and be the biggest thing in TV,” said Fox alternative topper Mike Darnell. “I look at those numbers and still can’t believe I can wake up in the seventh season of a TV show and see it do 12 million more viewers than the show next to it.

“There’s ‘Idol,’ and then there’s the rest of TV. I can’t look at it any other way.”

Darnell said he didn’t think the ratings dip mattered.

“This show has defied gravity for so long. After six years of being up every year, it’s almost like it’s a meaningless drop,” he said. “It’s such a juggernaut at this level that no one will ever want to compete with it.”

According to Nielsen national estimates that include same-night DVR playback, “American Idol” opened with a huge 13.8 rating/32 share among adults 18-49 and 33.42 million viewers overall from 8 to 10 p.m., building nicely with each half-hour. Those numbers put it down 13% from last year’s 15.8/36 in the demo — the best in the show’s seven seasons — and also 10% behind its second best score in 2006 (15.3/34).

In total viewers, this year’s kickoff average of 33.4 million reps an 11% decline from last year’s 37.4 million.

It’s worth noting that higher DVR penetration nationally could have contributed to some of the falloff, as roughly 10% more American homes have DVRs compared to a year ago. Although “Idol” is not a show that’s heavily TiVo’d, it stands to reason that the taped audition segs may draw more DVR action than the live performance and results shows down the road.

Tuesday’s demo delivery is a whopping 57% higher than the previous best same-night Nielsen score this season (8.8 rating/21 share for ABC’s season preem of “Grey’s Anatomy”), and “Idol’s” overall audience is 31% higher than the largest garnered for any other primetime series (25.4 million for the season preem of “CSI” on CBS.)

It also gave Fox the biggest night of television this season, surpassing last Saturday’s NFL playoff game between New England and Jacksonville on CBS.

Show remains extremely well balanced, drawing a 32 share among adults 18-49, a 31 share in adults 25-54 and a 35 share in persons 12-34. It was down vs. last year by about the same 13% in each category.

Biggest dropoff year to year came among women 18-34 (off 16%).

One possible explanation is that NBC’s weight-loss reality show “The Biggest Loser” (3.0/7 in 18-49, 7.18m) is a popular draw with this demo; the Peacock more than doubled its women 18-34 rating vs. the same night a year ago when it aired a newsmag and crime drama repeat (3.6 vs. 1.5).

CW’s “One Tree Hill” (1.3/3 in 18-49, 2.72m) gave young women another option in the 9 o’clock hour, with its rating in the demo (2.5) more than three times what a repeat of “Veronica Mars” managed in the slot last year on the netlet (0.8).

Elsewhere, “NCIS” (3.0/7, 15.82m) couldn’t take advantage of “Idol’s” decline, falling 19% year to year itself, though it remained No. 2 in the 8 o’clock hour.

ABC was the net putting up the least resistance opposite “Idol,” with its combo of “Just for Laughs” and half-hour comedies averaging a measly 1.1/3 in 18-49 and about 4 million viewers overall.

NBC’s “Law & Order: SVU” (4.6/12 in 18-49, 12.21m) dominated after “Idol” signed off at 10 o’clock.

(Michael Schneider contributed to this report.)