TV Ratings: 'The Office' Return Dips, 'The Big Bang Theory' Tops Thursday

UPDATED: NBC's "Whitney" and "Prime Suspect" start modestly, while ABC's "Grey's Anatomy" drops 24 percent on a night when "X Factor" holds up.

The competition is getting fierce on Thursday nights.

Fox topped the night with the second episode of The X Factor (12.5 million total viewers, 4.3 rating in adults 18-49 demographic). Simon Cowell's new reality competition series tied its series debut on Wednesday in total viewers and retaining most of its demo (4.3 vs. 4.4). So far this week, the network has notched victories for three of the four nights of the fall season. (Tuesday, Wednesday, Thursday).

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Still, it was CBS' premiere of The Big Bang Theory (14.1 million, 4.8 and 14.7 million, 5.0) -- the show, airing back-to-back episodes and celebrating Jim Parson's second Emmy win -- that took the crown as the night's highest-rated and most-watched program for its 8:30-9 p.m. telecast. Person of Interest (13.2 million, 3.1), the high-concept drama from J.J. Abrams and Jonathan Nolan was down 9 percent compared to CSI's premiere, but ranked as the most-watched program at 9 p.m. At 10 p.m., The Mentalist (13.6 million, 2.8), down 18 percent from its premiere last year, still won the night in total tune-in. CBS was No. 2 in the demo, averaging a 3.6, but continued to fulfill its name of the "most-watched network," averaging a Thursday high: 13.6 million.

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ABC's Charlie's Angels reboot (8.7 million, 2.1), though performing well above the launch of My Generation last September, didn't exactly strike a chord with viewers. The two-hour premiere of Grey's Anatomy (10.3 million, 4.1) dipped 24 percent and ranks as the veteran medical drama's lowest-premiere to date.

NBC's Thursday night comedy lineup all saw decreases from last year, with most hitting lows for its season openers: Community (4 million, 1.7) dipped 23 percent, Parks & Recreation (4.1 million, 2.0) was down 38 percent and The Office (7.6 million, 3.9), with the reveal of a new branch manager and the first episode of James Spader's as a regular, saw a 11 percent drop. The eighth season opener of The Office is its lowest-rated since the first season.

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Even Whitney (6.1 million, 3.2) didn't improve upon the debut of work comedy Outsourced, which was canceled after one season, down 11 percent. The lull affected the launch of new series Prime Suspect (6 million, 1.8), the U.S. reboot with Maria Bello, which barely contended with its competition (The Mentalist, Grey's Anatomy) at 10 p.m.

Up against heavy competition, the CW dramas The Vampire Diaries (2.5 million, 1.2) and The Secret Circle (2 million, 0.9) both saw steep drops.