On a Wednesday that saw key series on ABC and CBS air repeats, Fox’s “American Idol” was in line with last week and dominated its two hours while NBC’s “Chicago Fire” capped the night with a demo victory.

“American Idol” averaged a 5.4 rating/14 share in adults 18-49 and 15.6 million viewers overall, according to preliminary national estimates from Nielsen, down a tick in the demo and remaining easily the night’s No. 1 program.

From 8 to 10 p.m., the music contest topped the combined 18-49 scores of CBS (1.9), ABC (1.7) and NBC (1.4).

And similarly to previous episodes this season, “Idol” retained most of its 18-49 audience from the comparable show a year ago while rising a bit from last year in adults 18-34.

CBS ran second among the networks without any of its Wednesday originals. The net opened with the annual special “Super Bowl’s Greatest Commercials” (2.1/6 in 18-49, 9.9 million viewers overall), which was up from last year, and closed with encores of “Criminal Minds” (1.6/4 in 18-49, 7.2 million viewers overall) and “CSI” (1.6/4 in 18-49, 7.2 million viewers overall).

NBC, whose Wednesday lineup had aired repeats the past two weeks, returned to originals of low-rated comedies “Whitney” (1.3/4 in 18-49, 3.6 million viewers overall) and “Guys With Kids” (1.1/3 in 18-49, 2.9 million viewers overall). They were followed by a below-average “Law & Order: SVU” (1.7/4 in 18-49, 6.4 million viewers overall), which eked past the “Criminal Minds” repeat in 18-49, and another good outing at 10 p.m. for rookie “Chicago Fire” (2.0/6 in 18-49, 7.2 million viewers overall). Though down a bit from its most recent original of three weeks ago, “Fire” has now drawn three of its top four demo scores to date this month as well as its three largest overall audiences.

Next week will pose a tougher challenge for “Fire” as CBS’ “CSI” and ABC’s “Nashville” return to originals, but it’s clear that “Chicago Fire,” which looked shaky earlier this season, has found its groove.

ABC went with a mix of repeats and originals, starting with an encore “The Middle” (1.3/4 in 18-49, 5.5 million viewers overall) and a new “The Neighbors” (1.6/4 in 18-49, 5.2 million viewers overall), with the latter falling to a low without its usual lead-in but still easily topping NBC’s competing comedy in the half-hour. The net’s top score of the night came for an encore of “Modern Family” (2.1/5 in 18-49, 6.2 million viewers overall), which was followed by an original “Suburgatory” (1.8/5 in 18-49, 4.9 million viewers overall), which also was at a low without its typical lead-in support, and a repeat “Nashville” (0.9/3 in 18-49, 5.4 million viewers overall).

At CW, “Arrow” was down (0.9/3 in 18-49, 3.0 million viewers overall) and “Supernatural” held steady (0.9/2 in 18-49, 2.3 million viewers overall).

Preliminary 18-49 averages for the night: Fox, 5.4/14; CBS, 1.8/5; NBC, 1.6/4; ABC, 1.5/4; Univision, 1.5/4; CW, 0.9/2.

In total viewers: Fox, 15.6 million; CBS, 8.1 million; NBC, 5.6 million; ABC, 4.6 million; Univision, 3.6 million; CW, 2.6 million.