ABC’s ”Glass House,” the subject of a recent CBS copyright lawsuit, opened to soft numbers Monday, a night that was instead led by longtime reality staples ”America’s Got Talent” on NBC and ”Hell’s Kitchen” on Fox.

According to preliminary national estimates from Nielsen, ”Glass House” averaged a 1.6 rating/4 share and 4.2 million viewers overall in the 10 o’clock hour Monday, finishing behind both NBC and CBS in various categories as those nets sought to step up their presence in the timeslot in wake of the new show. NBC bypassed its usual repeat of ”Grimm” at 10 p.m. by extending ”American Ninja Warrior” by an hour, and CBS dumped its usual ”Hawaii Five-0” repeat for a pair of comedy repeats that fared better in the demo than the drama.

”Glass House,” which CBS believes is a ripoff of its long-running ”Big Brother,” fell in its second half-hour. Airing after ”The Bachelorette” (2.3/7 in 18-49, 6.9 million viewers overall), ”Glass House” opened with a 1.7/5 in the demo and 4.7 million viewers overall but fell to a 1.4/4 and 3.7 million in its second half-hour; its overall averages could come down further in the nationals since its preliminary hourlong score includes a two-minute runover from ”The Bachelorette.” Even as it stands now, the premiere of ”Glass House” was about 20% lower than the net’s episode of ”Extreme Makeover: Weight Loss Edition” a year ago and came in lower-rated than every episode of ”Big Brother” to air last summer on CBS.

Elsewhere, NBC’s ”America’s Got Talent” was Monday’s top program (2.8/9 in 18-49, 11.2 million viewers overall) but was down from its most recent airing on the night two weeks ago. And from 9 to 11, ”American Ninja Warrior” (2.0/5 in 18-49, 5.8 million viewers overall) was also down from two weeks ago but led its second hour in key demos.

Fox’s ”Hell’s Kitchen” (2.5/8 in 18-49, 5.6 million viewers overall) and ”Masterchef” (2.3/6 in 18-49, 5.5 million viewers overall) were down from last week when NBC preempted its reality shows for hockey’s Stanley Cup Finals. The cooking shows led their timeslots in men 18-49.

CBS aired a night of all-repeat comedies, with its top scores coming in the 10 p.m. hour from the special ”The Big Bang Theory” (1.8/5 in 18-49, 6.6 million viewers overall) and ”Two and a Half Men” (1.4/4 in 18-49, 4.9 million viewers overall).

Preliminary 18-49 averages for the night: Fox, 2.4/7; NBC, 2.3/7; ABC, 2.0/6; Univision, 1.4/4; CBS, 1.3/4; CW, 0.2/0.

In total viewers: NBC, 7.6 million; ABC, 6.0 million; Fox, 5.6 million; CBS, 5.2 million; Univision, 3.5 million; CW, 0.6 million.