Though “The Big Bang Theory” continued to trump “American Idol” in the first 30 minutes of primetime Thursday, Fox’s singing competition had no problem delivering the network a victory for the night.

Each of the broadcast networks remain bedeviled by an overall drop in TV viewing that has occurred most of the week, raising questions about whether something might be going wrong with the Nielsen numbers, but ongoing trends remained much the same.

According to preliminary nationals from Nielsen, “Big Bang” (5.0 rating/15 share in 18-49, 15.5 million viewers overall) aped other programs in showing a week-to-week drop, but still outdrew “American Idol” by a 0.4 rating in the demo and 500,000 viewers from 8-8:30 p.m.

“Idol” (5.0/13, 16.5 million from 8-10 p.m.) peaked from 8:30-9 p.m., though CBS’ 8:30 p.m. sitcom “Rob” (3.2/9, 10.9 million) actually came close to matching its week-earlier numbers.

With “30 Rock” (1.4/4, 3.6 million) and “Parks and Recreation” (1.7/5, 3.5 million), NBC barely held off ABC’s “Wipeout” (1.5/4, 5.1 million) for third place in the first hour of primetime among viewers 18-49 (at least among English-language networks: Univision’s broadcast of Latin music awards special “Premio Lo Nuestro” averaged a steady 2.1/6 in the demo and 5.1 million viewers overall from 8-11 p.m.).

CBS slipped to third place in the demo at 9 p.m. with “Person of Interest” (2.9/7, 13.2 million), which fell behind “Idol” and ABC’s “Grey’s Anatomy” (3.1/8, 8.1 million). NBC was fourth in the hour, with “The Office” (2.2/6, 4.3 million) hitting a series low and “Up All Night” (1.5/4, 3.0 million) still shedding more than 30% of its lead-in.

The 10 p.m. trophy for winning viewers 18-49 went to CBS’ “The Mentalist” (2.7/7, 13.5 million), which edged ABC’s “Private Practice” (2.6/7, 7.1 million) NBC aired the night’s only rerun, an episode of “Grimm” (the Friday drama that is serving as a placeholder until “Awake” premieres in March) that was broadcast’s lowest-rated offering in the demo (0.7/2, 2.0 million).

The CW offered “The Vampire Diaries” (1.3/4, 2.9 million) and “The Secret Circle” (0.8/2, 1.8 million).

Preliminary 18-49 averages for the night: Fox 5.0/13, CBS 3.3/9, ABC 2.4/6, Univision 2.1/6, NBC 1.4/4, CW 1.0/3.

In total viewers: Fox 16.5 million, CBS 13.4 million, ABC 6.8 million, Univision 5.1 million, NBC 3.1 million, CW 2.3 million.