CBS comedy smash ”The Big Bang Theory” was far and away primetime’s top-rated program on Thursday, powering the net to a demo victory over Fox, which saw declines for ”The X Factor.” With ABC’s ”Grey’s Anatomy” on the sidelines, Fox’s ”Bones” and CBS’ ”Person of Interest” were the night’s top dramas in demos.

According to preliminary national estimates, the first CBS Thursday victory of the season in adults 18-49 was paced by a big showing by ”The Big Bang Theory” (5.2/15 in 18-49, 14.8 million viewers overall), which was up nearly 20% from the same night last year, and a winning perf at 8:30 p.m. by ”Rules of Engagement” (3.6/10 in 18-49, 11.0 million viewers overall), which itself fared 20% better than ”Bleep My Dad Says” in the timeslot a year ago. The comedies were followed by dramas ”Person of Interest” (2.6/7 in 18-49, 11.6 million viewers overall) and ”The Mentalist” (2.5/7 in 18-49, 12.1 million viewers overall), both down about 15% from last year’s 9-11 p.m. dramas (”CSI” and ”Mentalist”) still, ”Person” was the No. 1 drama of the night in adults 25-54 (3.7/8).

At Fox, ”The X Factor” was on the low side (3.0/8 in 18-49, 9.5 million viewers overall), placing second in the 8 o’clock hour and jumping sharply in its second half-hour (3.4 vs. 2.7). The net then moved to the 18-49 lead at 9 o’clock with ”Bones” (2.8/7 in 18-49, 8.8 million viewers overall), which took advantage of ”Grey’s Anatomy’s” absence to grow week to week and lead all dramas for the night in 18-49.

ABC helped its cause by airing a Katie Couric ”20/20” special on Regis Philbin (1.5/4 in 18-49, 8.0 million viewers overall), which performed about 35% better than last week’s episode of ”Charlie’s Angels” in the timeslot. The special was followed by a two-hour episode of ”Private Practice” (2.5/7 in 18-49, 7.2 million viewers overall), which was down from its hourlong averages of last week but still edged out ”The Mentalist” as the top-rated 10 p.m. broadcast series in 18-49.

At NBC, ”Community” (1.6/5 in 18-49, 3.6 million viewers overall) and ”Parks and Recreation” (2.0/5 in 18-49, 3.7 million viewers overall) were up week to week, finishing ahead of ABC’s ”20/20” special in demos. They were followed by ”The Office” (2.9/7 in 18-49, 4.1 million viewers overall), which was in line with last week and led its half-hour in 18-49, and ”Whitney” (1.9/5 in 18-49, 4.1 million viewers overall), down a couple of ticks week to week. Also down was outgoing 10 p.m. drama ”Prime Suspect” (1.1/3 in 18-49, 4.4 million viewers overall).

CW rested dramas ”The Vampire Diaries” and ”The Secret Circle,” and went with theatrical ”Beneath the Blue” (0.8/2 in 18-49, 2.6 million viewers overall). Numbers for the pic, which stars Paul Wesley of ”Vampire Diaries,” are subject to revision since the affiliate-based preliminaries include preemptions in Denver and New York for NFL action.

Preliminary 18-49 averages for the night: CBS, 3.2/8; Fox, 2.9/8; ABC, 2.2/6; NBC, 1.8/5; Univision, 1.6/4; CW, 0.8/2.

In total viewers: CBS, 12.2 million; Fox, 9.1 million; ABC, 7.5 million; NBC, 4.3 million; Univision, 3.7 million; CW, 2.6 million.