The unstoppable combo of “American Idol” and “House” carried Fox to an easy ratings victory on Tuesday night, although “Idol” again came in about 10% below last year’s ratings levels. NBC, meanwhile, held tough with “Biggest Loser” and “Law & Order: SVU.”

According to preliminary nationals from Nielsen, “American Idol” dominated the night’s opening hour with an 11.7 rating/29 share in adults 18-49 and 29.1 million viewers overall. It beat its combined ABC-CBS-NBC competition by 13 shares in the demo despite coming in a bit more than 10% below its scores on the same night a year ago. Fox remained on top at 9 o’clock with a repeat of “House” (5.1/12 in 18-49, 14.0 million viewers overall).

Over at NBC, a two-hour episode of “Biggest Loser” (3.7/9 in 18-49, 8.9 million viewers overall) was up vs. last week, when it aired opposite the two-hour “Idol” premiere, and ran second to Fox in both hours. From 8 to 9, its 2.9 rating among 18-49ers reps the best for NBC in the hour opposite “Idol” in nearly two years. The Peacock then stormed to the lead at 10 p.m. with a new episode of “Law & Order: Special Victims Unit” (4.6/12 in 18-49, 13.0 million viewers overall).

CBS didn’t do much on the night, delivering about the same demo score each hour with repeats of “NCIS” (2.1/5 in 18-49, 12.2 million viewers overall) and “The Unit” (1.9/5 in 18-49, 7.9 million viewers overall) and a new edition of newsmag “48 Hours Mystery” (2.0/5 in 18-49, 6.9 million viewers overall).

ABC struggled too with its lineup of “Just For Laughs” (1.4/4 in 18-49, 4.8 million viewers overall), 9 o’clock hour comedies “According to Jim” (2.2/5 in 18-49, 6.2 million viewers overall) and “Carpoolers” (1.7/4 in 18-49, 4.9 million viewers overall) and 10 o’clock drama “Boston Legal” (2.2/6 in 18-49, 8.2 million viewers overall).

CW did nothing at 8 o’clock opposite “Idol” with a repeat of “Reaper” (0.6/1 in 18-49, 1.5 million viewers overall) but shot up at 9 o’clock with “One Tree Hill” (1.3/3 in 18-49, 3.1 million viewers overall), which ranked third for its hour among persons 12-34 (1.9/5) and females 12-34 (2.6/7).

Preliminary 18-49 averages for the night: Fox, 8.4/20; NBC, 4.0/10; CBS, 2.0/5; ABC, 1.8/5; Univision, 1.8/4; CW, 1.0/2.

In total viewers: Fox, 21.5 million; NBC, 10.3 million; CBS, 9.0 million; ABC, 6.2 million; Univision, 4.1 million; CW, 2.3 million.