SECOND UPDATE: As expected, Big Bang was adjusted up to a 5.3 demo rating in the finals, edging Idol‘s 5.2 from 8-8:30 PM.

UPDATE: In the time-adjusted fast nationals, American Idol went up a tenth to a 5.7 in 18-49 from 8-9 PM and tied The Big Bang Theory’s non-time zone-adjusted 5.2 demo fast-national rating from 8-8:30 PM. But Big Bang too is projected to go up a tenth in the finals to a 5.3, so the standings in the half-hour are expected to remain the same.

PREVIOUS: After ABC’s Modern Family on Wednesday logged its best ratings ever against American Idol, CBS’ The Big Bang Theory did one better last night, besting the Fox reality juggernaut for the first time. Big Bang‘s 100th episode drew a 5.2/14 in 18-49, even with its fast national rating last week. It edged Idol‘s 5.1 demo rating from 8:30 PM. Idol grew to a 6.1 from 8:30-9 PM to top the night with a 5.6/15 in 18-49. But, just like on Wednesday, Idol was down sharply from last year, 28% from its Thursday premiere (20% from the 8-9 PM hour). With Idol as a lead-in, new Fox drama The Finder (2.2/5) was up 29% from its underwhelming premiere last week, but it still held onto a paltry third of the Idol 8:30-9 PM demo rating. Fox (3.9/10, 12.3 million) won the night in 18-49 but not in total viewers, with CBS (3.5/9, 14.0 million) topping that.

Besides Big Bang, only NBC’s Parks And Recreation was not pushed down by Idol in the 8 PM hour. In Week 2, CBS’ new comedy Rob (3.6/9) was down a modest 12% considering it faced the second half of Idol. ABC’s Wipeout (1.8/5) was down 18%. NBC’s 30 Rock (1.6/4), which featured a storyline riffing on last year’s controversy stirred by star Tracy Morgan’s use of gay slur in a standup routine, was down 11% from its season premiere last week to a series low. Parks And Rec (2.9/5) was up 5%.

At 9 PM, CBS rookie drama Person Of Interest (3.3/8) was up a tenth from last week to hit a series high in 18-49, while veteran Mentalist (2.9/8) was up 7%. ABC’s Grey’s Anatomy (3.4/8) was down 11% from last week, while Private Practice (2.1/5) was down 9%. NBC’s The Office (2.9/7) was flat, while Up All Night (1.9/5) does not seem to be feeling comfortable in its new Thursday 9:30 PM slot, down 5% from last week. Not much to say about The Firm (0.9/2), which was down another tenth and was soundly beaten by the CW’s Vampire Diaries (1.1/3), which was down a modest 8% (a tenth) against Idol. The Secret Circle (0.7/2) was down 12%, also a tenth.