On an atypical Thursday, with an expanded “American Idol” accounting for all of Fox’s programming, the net pulled ahead of CBS to prevail in key demos. Still, the Eye’s “The Big Bang Theory” crushed “Idol” head-to-head and was easily the night’s No. 1 show.

According to preliminary Nielsen estimates, the two-hour Sudden Death round episode of “American Idol” averaged a 3.9 rating/10 share in adults 18-49 and 13.5 million viewers overall — up 5% from its one-hour average of last week and good enough to win its final three half-hours in adults 18-49. From 8 to 10 p.m., “Idol” edged out CBS in 18-49 (3.9 to 3.8), while the Eye led in 25-54 and total viewers.

“Idol” will also play for two hours next Thursday, with “Glee” set to resume in its 9 p.m. timeslot on March 7.

Elsewhere, CBS had another monster start to the night with “The Big Bang Theory” (5.4/16 in 18-49, 17.3 million viewers overall), which was in line with last week and beat “Idol” head-to-head by 50% in 18-49 (5.4 to 3.6). From there, “Two and a Half Men” (3.9/11 in 18-49, 13.4 million viewers overall) was up a tick from last week and nearly caught “Idol” for the 18-49 lead at 8:30 p.m., and “Person of Interest” (2.9/8 in 18-49, 14.1 million viewers overall) and “Elementary” (2.3/6 in 18-49, 11.0 million viewers overall) were about on par with last week; “Elementary” won the 10 p.m. hour in 25-54 and total viewers.

CBS ranked second on the night to Fox in 18-49 and 25-54; the nets were neck and neck in total viewers.

Univision ranked third on the night in 18-49 (2.5/7) with its 25th-anniversary edition of Latin music awards show “Premio Lo Nuestro,” which drew 5.8 million viewers overall from 8 to 11.

At ABC, “Zero Hour” (1.1/3 in 18-49, 5.3 million viewers overall) declined about 20% from last week’s soft series premiere, but the net spiked as usual at 9 p.m. with “Grey’s Anatomy” (3.0/8 in 18-49, 8.5 million viewers overall), which was up a bit from last week (despite the presence of “American Idol” in its hour) and moved back ahead of CBS’ “Person of Interest” in 18-49 (3.0 vs. 2.9). And at 10, “Scandal” (2.7/7 in 18-49, 7.6 million viewers overall) continues to perform well, in line with last week and again winning its hour in 18-49.

It was another rough night for NBC, where “Community” (1.1/3 in 18-49, 3.1 million viewers overall) matched its modest week-ago preliminary score, and “Parks and Recreation” couldn’t do much with its hourlong episode; its regular-slot 8:30 p.m. half-hour hit a series low (1.3/4 in 18-49, 3.0 million viewers overall) and the concluding 9 p.m. half-hour fared about the same (1.4/4 in 18-49, 2.9 million viewers overall). Closing out the night were first-year half-hour “1600 Penn” (1.0/3 in 18-49, 2.3 million viewers overall) and a repeat of “Law & Order: SVU” (1.1/3 in 18-49, 3.9 million viewers overall), which delivered a five-week high for the net at 10 o’clock.

CW had a good start to the night with “The Vampire Diaries” (1.3/4 in 18-49, 2.9 million viewers overall), which bounced back from its sub-par outing on Valentine’s Day and beat out in 18-49 both ABC’s “Zero Hour” and NBC’s comedy block. And up a tick at 9 p.m. was rookie “Beauty and the Beast” (0.6/1 in 18-49, 1.6 million viewers overall).

Preliminary 18-49 averages for the night: Fox, 3.9/10; CBS, 3.3/9; Univision, 2.5/7; ABC, 2.2/6; NBC, 1.2/3; CW, 0.9/2.

In total viewers: CBS and Fox, 13.5 million; ABC, 7.2 million; Univision, 5.8 million; NBC, 3.2 million; CW, 2.2 million.