This week’s “American Idol” results show, which produced the 12 finalists for this year’s competition, lifted Fox to a primetime victory among adults 18-49 on an uneventful Thursday, according to preliminary nationals from Nielsen.

Meanwhile, NBC’s “The Marriage Ref” declined 21% in its 18-49 rating from last week’s official series premiere.

“Idol” (6.2 rating/18 share in 18-49, 19.1 million viewers overall) had no trouble topping CBS’ “Survivor” (3.6/11, 12.1 million) at 8 p.m. NBC comedies “Community” (1.9/6, 4.7 million) and “Parks and Recreation (2.1/6, 4.6 million) suffered slight week-to-week declines. “Parks,” which slightly trailed “Community” earlier this season, now seems to have caught up and passed it in the demo.

Reruns of “Grey’s Anatomy” (1.1/3, 4.4 million) on ABC and “The Vampire Diaries” (0.5/2, 1.5 million) on the CW at 8 p.m. drew little attention from those 18-49.

In the 9 p.m. hour, a firstrun “Grey’s” (3.9/11, 11.0 million) was tops, though NBC’s “The Office” (3.8/11, 7.5 million) matched “Grey’s” in 18-49 from 9-9:30 p.m. In the most competitive hour of the night, CBS’ “CSI” (3.3/9, 15.4 million) drew the biggest overall aud, while Fox’s “Kitchen Nightmares” (3.1/9, 7.6 million) was also competitive in the demo.

The first post-Olympics episode of “30 Rock” (2.9/8, 5.9 million) lost nearly 25% of its “Office” leadin at 18-49, though it was No. 1 in key male demos. A repeat of the CW’s “Supernatural” (0.5/1, 1.4 million) trailed.

Last week, boosted by a special hourlong episode of “The Office,” the Peacock’s “Ref” won the 10 p.m. hour in the demo — but this week “Ref” came in third (2.7/8, 6.0 million). CBS’ “The Mentalist” (3.4/10, 16.0 million) was the winner in 18-49 and overall, while a firstrun “Private Practice” (2.9/9, 7.9 million) on ABC was second.

In latenight, “The Tonight Show with Jay Leno” and “Late Show with David Letterman” tied in metered-market households with a 3.2/8.

Preliminary 18-49 averages: Fox 4.7/13, CBS 3.4/10, NBC 2.7/8, ABC 2.6/8, Univision 1.3/4, CW 0.5/2.

In total viewers: CBS 14.5 million, Fox 13.4 million, ABC 7.8 million, NBC 5.8 million, Univision 3.4 million, CW 1.4 million.