Fox’s “American Idol” may not be kicking off its seventh season as big as last year, but it’s decimating the competition. On Wednesday, another two-hour auditions episode nearly doubled the combined ABC-CBS-NBC competition, as reality shows on those nets showed significant week-to-week declines.

According to preliminary nationals from Nielsen, “American Idol” averaged a big 12.6 rating/30 share in adults 18-49 and 30.3 million viewers overall from 8 to 10 p.m., dipping 9% from Tuesday’s season premiere and 19% from its first Wednesday edition of last season. Despite the dropoff, Fox’s 30 share in the demo during “Idol” was nearly double the 16 combined share for the other major networks.

ABC’s “Wife Swap” (2.0/5 in 18-49, 5.2 million viewers overall) and “Supernanny” (2.5/6 in 18-49, 6.1 million viewers overall) were both down by about 30% vs. their solid scores of the previous week, while struggling CBS gameshow “Power of 10” (1.1/3 in 18-49, 4.9 million viewers overall) tumbled by more than 30% itself in the 8 o’clock hour.

The show holding up best opposite “Idol” was NBC gameshow “Deal or No Deal” (3.1/8 in 18-49, 11.8 million viewers overall), which slid by 14% week to week to place second in the opening hour and improved upon its performance on the same night a year ago (when it aired at 9 p.m.) by a considerable 41% (3.1 vs. 2.2). Combined with “Law & Order: Criminal Intent” in the 9 o’clock hour (2.4/5 in 18-49, 8.8 million viewers overall), NBC scored its best non-Olympics 18-49 average ever (2.7) opposite a two-hour Wednesday “Idol.”

The Peacock also won the 10 o’clock hour with an original episode of “Law & Order” (3.6/9 in 18-49, 11.6 million viewers overall), finishing well ahead of ABC drama “Cashmere Mafia” (2.2/6 in 18-49, 5.4 million viewers overall). At CBS, the conclusion of three-night miniseries “Comanche Moon” averaged a 2.4/6 in 18-49 and 12.1 million viewers overall from 9 to 11 p.m.

Preliminary 18-49 averages for the night: Fox, 12.6/30; NBC, 3.0/7; ABC, 2.2/5; CBS, 2.0/5; Univision, 1.6/4; CW, 0.6/1.

In total viewers: Fox, 30.3 million; NBC, 10.7 million; CBS, 9.7 million; ABC, 5.5 million; Univision, 3.4 million; CW, 1.4 million.