CBS aired repeats Monday, opening things up for rival nets to post some ratings gains. Fox’s ”House” returned from its hiatus a winner, and the net’s ”Alcatraz” held onto most of its premiere audience in its second outing.

According to preliminary national estimates from Nielsen, ”House” (3.1 rating/8 share in adults 18-49, 8.7 million viewers overall) led the 8 o’clock hour in all categories, rising 19% from its most recent original in late November. It was followed by the second week of ”Alcatraz” (3.0/7 in 18-49, 9.0 million viewers overall), which looked like a good fit with ”House” and retained about 90% of its premiere-week audience; it joins Fox’s ”Terra Nova” and ABC’s ”Once Upon a Time” as the season’s only dramas this season to have earned a 3 demo rating or higher in their second telecast.

Fox won the night in 18-49, 25-54 and total viewers.

ABC moved up to second in demos as ”The Bachelor” (2.7/7 in 18-49, 8.2 million viewers overall) grew 13% week to week for a season high. At 10 p.m., drama ”Castle” (2.1/5 in 18-49, 10.1 million viewers overall) was down a tick week to week in 18-49 and grew some in total viewers, leading the broadcast pack in both categories.

CBS was competitive with repeats of comedies ”How I Met Your Mother” (2.3/6 in 18-49, 7.0 million viewers overall), ”2 Broke Girls” (2.6/6 in 18-49, 7.8 million viewers overall), ”Two and a Half Men” (2.9/7 in 18-49, 9.8 million viewers overall) and ”Mike and Molly” (2.4/6 in 18-49, 8.3 million viewers overall), followed by an encore ”Hawaii Five-0” (1.6/4 in 18-49, 6.8 million viewers overall).

NBC saw gameshow ”Who’s Still Standing” edge up to its best Monday demo score to date (1.7/4) while drawing its largest overall audience for any night (6.4 million). And from 9 to 11, a Republican candidates debate airing on ”Rock Center with Brian Williams” averaged a 1.6/4 in 18-49 and 7.1 million viewers overall, ranking third or fourth among the broadcasters in most categories from 9 to 11 but up from its regular 10 p.m. telecast of last week.

CW’s ”Gossip Girl” (0.7/2 in 18-49, 1.6 million viewers overall) and ”Hart of Dixie” (0.7/2 in 18-49, 1.6 million viewers overall) posted identical averages, with the former up and the latter down a tick vs. their most recent original episodes. (Due to a preemption in Chicago for Bulls basketball, the net’s numbers are subject to revision in the nationals.)

Preliminary 18-49 averages for the night: Fox, 3.0/8; ABC, 2.5/6; CBS, 2.2/6; NBC, 1.7/4; Univision, 1.6/4; CW, 0.7/2.

In total viewers: ABC and Fox, 8.8 million; CBS, 7.7 million; NBC, 6.9 million; Univision, 3.7 million; CW, 1.6 million.