CBS summer stalwart ”Big Brother” opened its 14th season with good numbers Thursday, off slightly from last year’s hot start but easily the top-rated among the night’s eight original programs on the major broadcast nets. Also of note, NBC’s ”Rock Center” hit a six-month high.

According to preliminary national estimates from Nielsen, ”Big Brother” averaged a 2.6 rating/8 share in adults 18-49 and 7.1 million viewers overall in the 9 o’clock hour , down from last year’s 2.8/8 in the demo, which had been the show’s top-rated premiere in four years. ”Brother” will once again air three times a week, with its other two regular timeslots on Sunday and Wednesday at 8.

”Brother” actually dropped off from its lead-in from a repeat of ”The Big Bang Theory” (2.8/8 in 18-49, 9.0 million viewers overall), which was Thursday’s top-rated program and doubled up the delivery of the year-ago’s repeat of ”Rules of Engagement” in the timeslot. The regular 8 p.m. repeat of ”The Big Bang Theory” dominated its timeslot as well (2.3/8 in 18-49, 8.0 million viewers overall), rising about 20% year-to-year. Closing out the night, which CBS led in all categories, was an encore of ”Person of Interest” in its new summer timeslot of 10 p.m. (1.2/4 in 18-49, 5.6 million viewers overall).

Univision ranked second for the night among young adults, as 10 p.m. novela ”La Que No Podia Amar” (The One Who Couldn’t Love) again topped its hour in demos (1.7/5 in 18-49, 4.4 million viewers overall) and showed gains vs. its recent performances.

At NBC, ”Rock Center With Brian Williams” (1.2/4 in 18-49, 5.2 million viewers overall) shot up 33% week to week, delivering the show’s best numbers since Jan. 23 thanks to a segment on the role of the Church of Scientology in the Tom Cruise-Katie Holmes split; in its second half-hour, ”Rock” ruled among the major networks in all key categories. Not so hot for the Peacock on Thursday were comedy repeats ”The Office” (0.6/2 in 18-49, 2.1 million viewers overall) and ”Parks and Recreation” (0.6/2 in 18-49, 1.7 million viewers overall), followed by original 9 p.m. drama ”Saving Hope” (0.5/2 in 18-49, 3.2 million viewers overall).

Fox’s celebrity dating show ”The Choice” ended its first season on a quiet note (1.2/4 in 18-49, 3.0 million viewers overall), down 25% from last week when it didn’t face ”Big Brother.” It matched the score of its lead-in from ”Take Me Out” (1.2/4 in 18-49, 3.0 million viewers overall), which held steady week to week.

At ABC, ”Duets” (1.0/3 in 18-49, 5.2 million viewers overall) matched its low demo score of last week while adding more overall viewers. It was followed by ”Wipeout” (1.7/5 in 18-49, 5.2 million viewers overall), which was down a tick from its Thursday premiere of last week, and ”Rookie Blue” (1.3/4 in 18-49, 5.0 million viewers overall), which was steady and held a slim young-adult advantage over CBS and NBC in the 10 o’clock hour.

Preliminary 18-49 averages for the night: CBS, 2.1/7; Univision, 1.7/5; ABC, 1.3/4; Fox, 1.2/4; NBC, 0.8/2; CW, 0.3/1.

In total viewers: CBS, 7.1 million; ABC, 5.0 million; NBC, 3.4 million; Univision, 3.8 million; Fox, 3.0 million; CW, 0.8 million.