NBC couldn’t muster much interest for its new unscripted series “Celebrity Cooking Showdown,” which opened to a fourth-place finish Monday night. ABC was also underwhelming with the series premiere of “What About Brian.”

According to preliminary nationals from Nielsen, NBC started the night off strong as usual with a timeslot victory for “Deal or No Deal” (4.4/12 in 18-49, 15 million viewers overall) but then sunk to fourth with “Cooking Showdown” (2.9/7 in 18-49, 8.7 million viewers overall), which was off about 15% from what “The Apprentice 5” netted in the hour one week earlier. The soft perf affected “Medium,” which posted some of its lowest firstrun scores to date (3.8/10 in 18-49, 10.5 million viewers overall).

Fox won the night in demos thanks to “24” (5.5/13 in 18-49, 13.1 million viewers overall), which comfortably led the 9 o’clock hour, and a solid second-place showing by 8 o’clock drama “Prison Break” (3.5/10 in 18-49, 8.0 million viewers overall).

At ABC, “What About Brian” opened at 10 with a third-place 3.2/8 in 18-49 and 7.1 million viewers overall, down some from its third-place lead-in from “Supernanny” (3.6/9 in 18-49, 8.8 million viewers overall).

CBS was paced by a first-place perf at 10 for a repeat of “CSI: Miami” (4.9/13 in 18-49, 15.7 million viewers overall). New comedy “Old Christine” placed second at 9:30 (3.7/9 in 18-49, 11.5 million viewers overall), with similar scores to its repeat lead-in from “Two and a Half Men” (3.7/9, 12.1 million).

Preliminary 18-49 averages for the night: Fox, 4.5/12; CBS, 3.7/10; NBC, 3.7/10; ABC, 3.1/8; WB, 1.7/5; UPN, 1.4/4.

In total viewers: CBS, 11.6 million; NBC, 11.4 million; Fox, 10.5 million; ABC, 7.4 million; WB, 4.4 million; UPN, 3.2 million.