Fox’s “American Idol” held up well in its second week, declining 10% from its premiere to remain dominant on Wednesday in key demos. It was also a good night for CBS vet “CSI,” which hit a season high.

According to preliminary national estimates from Nielsen, “American Idol” averaged a 5.4 rating/15 share in adults 18-49 and 16 million viewers overall from 8 to 10 p.m., building to a 5.7/14 in the demo and 16.4 million viewers for its final half-hour when it beat the combined firstrun deliveries on CBS and ABC. Although these appear to be all-time lows for a January episode of the music contest, “Idol” was easily the night’s No. 1 show in all under-55 categories.

When the nationals come in, “Idol” is expected to be down about 15% in 18-49 from last year’s second Wednesday installment; the show’s premiere last week lagged its year-ago average by 19%. And this season’s decline from its first Wednesday to its second is smaller than last year.

Elsewhere, it was a mixed bag at ABC, where “The Middle” (2.5/7 in 18-49, 8.5 million viewers overall) and “The Neighbors” (1.9/5 in 18-49, 6.3 million viewers overall) were up a bit from last week, but “Modern Family” dipped to a same-night season low (4.1/11 in 18-49, 10.8 million viewers overall), but remained Wednesday’s top draw in 18-49 among scripted series. “Suburgatory” held steady at 9:30 (2.3/6 in 18-49, 6.3 million viewers overall) but “Nashville” (1.8/5 in 18-49, 5.5 million viewers overall) took a step back, inexplicably falling 18% week to week.

CBS followed a repeat “Criminal Minds” (1.5/4 in 18-49, 6.8 million viewers overall) with the regularly scheduled original (3.0/8 in 18-49, 11.7 million viewers overall), which was down from last year but up a tick from last week. Also down from last year but up from last week, and to a season high, was 10 p.m. vet “CSI” (2.7/7 in 18-49, 11.5 million viewers overall), which gained about what “Nashville” lost week to week.

NBC went with repeats of its Wednesday regulars: “Whitney” (0.8/2 in 18-49, 2.6 million viewers overall), “Guys with Kids” (0.8/2 in 18-49, 2.2 million viewers overall), “Law & Order: SVU” (0.7/2 in 18-49, 2.7 million viewers overall) and “Chicago Fire” (0.8/2 in 18-49, 2.5 million viewers overall). Net is back in originals next week.

At CW, “Arrow” (1.1/3 in 18-49, 3.1 million viewers overall) and “Supernatural” (0.9/2 in 18-49, 2.1 million viewers overall) continue to make for a solid pairing. These shows are skewing older than previous fare on the net, though, with “Arrow” not quite matching what “One Tree Hill” did in the hour a year ago in adults 18-34.

Still, for the night, the CW beat NBC’s encores in both 18-49 and 18-34.

Preliminary 18-49 averages for the night: Fox, 5.4/15; ABC, 2.4/7; CBS, 2.4/6; Univision, 1.6/5; CW, 1.0/3; NBC, 0.8/2.

In total viewers: Fox, 16.0 million; CBS, 10.0 million; ABC, 7.1 million; Univision, 3.8 million; NBC and CW, 2.6 million.