Repeats on CBS enabled ABC’s firstrun lineup to deliver a dominant ratings victory in key demo categories on Thursday, powered by “Grey’s Anatomy” in the night’s middle hour.

Acccording to preliminary Nielsen nationals, ABC’s “Grey’s Anatomy” (9.6 rating/23 share in adults 18-49, 24.3 million viewers overall) easily stood as the night’s top program, besting a repeat “CSI” on CBS (5.0/12 in 18-49, 15.9 million viewers overall) and NBC’s new comedy block of “Scrubs” (3.9/9 in 18-49, 8.4 million viewers overall) and “30 Rock” (3.0/7 in 18-49, 6.6 million viewers overall). “Scrubs,” in its season preem, delivered the net’s second best score in the 9 o’clock slot this season.

In the opening hour, CBS ruled with “Survivor: Cook Islands” (5.3/14 in 18-49, 15.5 million viewers overall), but NBC’s combo of “My Name Is Earl” (4.3/12 in 18-49, 10.0 million viewers overall) and “The Office” (4.6/11 in 18-49, 9.6 million viewers overall) were competitive, as was ABC’s “Ugly Betty” (4.1/11 in 18-49, 13.3 million viewers overall). These repped season-best scores for the Peacock laffers.

At 10, NBC’s “ER” won easily (6.0/16 in 18-49, 13.9 million viewers overall), followed by ABC’s “Men in Trees” (4.0/10 in 18-49, 11.9 million viewers overall) and CBS’ repeat of “Shark” (2.8/7 in 18-49, 10.4 million viewers overall). In its first try in the timeslot, “Men” — which had been airing on Friday — achieved season highs and delivered the best regular-program scores in the Thursday-at-10 slot for ABC since September.

Fox remained well behind the pack with comedy “Til Death” at 8 (1.9/5 in 18-49, 4.8 million viewers overall) and “The OC” at 9 (1.6/4 in 18-49, 3.6 million viewers overall).

Numbers for ABC and NBC could come down a bit in nationals, as the preliminary numbers include high-rated NFL coverage on those nets’ affils in Baltimore and Cincinnati, respectively.

Preliminary 18-49 averages for the night: ABC, 5.9/15; NBC, 4.7/12; CBS, 4.4/11; Fox, 1.8/4; Univision, 1.6/4; CW, 1.1/3.

In total viewers: ABC, 16.5 million; CBS, 13.9 million; NBC, 10.4 million; Fox, 4.2 million; Univision, 3.7 million; CW, 2.9 million.