NBC prevailed in key demos on Wednesday behind summer stalwart “America’s Got Talent,” which was again the night’s top-rated program. CBS and Fox both hung in there with their own reality vets, “Big Brother” and “So You Think You Can Dance,” respectively.

According to preliminary national estimates from Nielsen, “America’s Got Talent” averaged a 2.3 rating/7 share in adults 18-49 and 8.7 million viewers overall in the 9 o’clock hour, in line with its performance of last week; it was Wednesday’s No. 1 program in just about every category. The net also did decently with a repeat of “Talent” at 9 (1.5/5 in 18-49, 5.6 million viewers overall) and a rerun of “Law & Order: SVU” (1.3/4 in 18-49, 4.6 million viewers overall), which was the broadcast leader at 10.

CBS led the night’s opening hour with “Big Brother” (2.0/7 in 18-49, 5.8 million viewers overall), down a tick from last week. It was followed by repeats of “Criminal Minds” (1.3/4 in 18-49, 5.8 million viewers overall) and “CSI” (1.1/3 in 18-49, 5.7 million viewers overall).

At Fox, “So You Think You Can Dance” (1.5/5 in 18-49, 4.5 million viewers overall) fell off 17% week to week, placing third in 18-49 for its two-hour block.

ABC aired encores of comedies “The Middle” (1.1/4 in 18-49, 4.1 million viewers overall), “Suburgatory” (0.9/3 in 18-49, 3.3 million viewers overall) and “Modern Family” (1.2/4 in 18-49, 3.5 million viewers overall), followed by a second repeat of “Suburgatory” in its new fall timeslot (1.0/3 in 18-49, 2.6 million viewers overall). Closing out the night was the finale of “NY Med” (1.0/3 in 18-49, 4.4 million viewers overall), which was neck and neck with repeat crime dramas on CBS and NBC in adults 25-54 (1.5/4).

At CW, “Oh Sit” (0.4/1 in 18-49, 1.2 million viewers overall) held onto most of its premiere audience from a week earlier, and was followed by a special repeat of music talent show “The Next” (0.3/1 in 18-49, 0.7 million viewers overall), which did about as well as its original airing on Thursday of last week.

Preliminary 18-49 averages for the night: NBC, 1.7/5; CBS and Fox, 1.5/5; Univision, 1.3/4; ABC, 1.0/3; CW, 0.4/1.

In total viewers: NBC, 6.3 million; CBS, 5.7 million; Fox, 4.5 million; ABC, 3.7 million; Univision, 3.4 million; CW, 0.9 million.