As “American Idol” whittled its field down to a top 12, the show itself again claimed the top three spots in the weekly primetime rankings.

That, and a winning perf from Monday drama “House,” helped Fox score a victory in key demos. It was also a good week for CBS, which dominated the rest of the top 20 in demos and fared especially well in the final hour of primetime.

Despite the CBS success at 10 p.m. (claiming at least a share of the demo lead each weeknight), it was NBC’s “The Tonight Show With Jay Leno” that held the latenight advantage over CBS’ “Late Show With David Letterman” in the second week of their renewed rivalry (by a preliminary margin of 1.2 to 1.0 in 18-49 and 4.4 million to 3.8 million in total viewers).

Overall in primetime, according to Nielsen, Fox prevailed in adults 18-49 with a 3.4 rating/10 share, followed by CBS (2.8/8), ABC and NBC (both at 2.1/6) and Univision (1.2/4).

Fox also led narrowly over CBS in adults 25-54 (3.9/10 to 3.7/10) and dominated among persons 12-34 (2.7/9 to 1.6/6 for CBS), while the Eye reversed things in total viewers (11.3 million to 9.4 million for Fox).

“American Idol” performance hours on Tuesday (8.2/23 in 18-49, 22.75 million viewers overall) and Wednesday (7.5/20, 20.70m) dominated their respective hours, and the final Thursday results show of the season rolled over that night’s competition as well (6.3/19, 19.34m).

Show continues to hold up well — especially for a series in its eighth season. Nielsen’s “most current” averages show “Idol” down 7% year to year in 18-49 (9.4/24 vs. 10.1/25) and 6% in total viewers (25.1 million vs. 26.7 million).

Other highlights for Fox last week included Monday’s “House” (4.8/13 in 18-49, 12.81m), the week’s top drama in 18-49, and an improved perf for Wednesday rookie drama “Human Target” (2.4/7, 7.83m), which led its hour.

CBS, meanwhile, accounted for half of the week’s top 20 shows — twice as many as Fox (5) and also double the combined total for ABC (4) and NBC (1).

All four of the net’s Monday comedies ranked in the top 15, led by “The Big Bang Theory” (5.9/15 in 18-49, 16.32m) — which drew its largest overall aud to date — and “Two and a Half Men” (5.8/15, 17.61m), which logged its best 18-49 score in three years.

The combo of “The Amazing Race” (3.0/9 in 18-49, 10.10m) and “Undercover Boss” (3.9/10, 13.51m) continue to work well together on Sunday, winning their hours and pacing the net’s first 18-49 victory on the night (with and against regular programming) since fall 2004.

And the net’s 10 p.m. hour was highlighted by victories on Tuesday for “The Good Wife” (2.8/9, 13.95m) and Thursday for “The Mentalist” (3.4/10, 16.02m).

ABC was led by “Lost” (4.2/11 in 18-49, 9.49m), “Grey’s Anatomy” (3.9/11, 10.94m), “Modern Family” (3.8/10, 9.02m) and “Desperate Housewives” (3.7/9, 12.01m) — each the top scripted program in 18-49 on their respective nights.

Net was dragged down, though, by weak showings Friday, where the finale of “Supernanny” settled for a 1.1/4 in 18-49, and Saturday, where repeats of “Desperate Housewives” and “Jimmy Kimmel Live” left the net 13th for the night (0.5/2).

At NBC, where “Parenthood” (2.6/8 in 18-49, 6.09m) and “The Marriage Ref” (2.6/8, 6.01m) declined following their solid debuts, the lone top 20 performer was “The Office” (3.8/11 in 18-49, 7.43m).

Later in the week, the net had reason to be pleased with unscripted performers “Who Do You Think You Are” (1.7/6, 6.95m), “Minute to Win It” (2.4/7, 7.47m for its regular 8 p.m. hour) and “Celebrity Apprentice” (3.2/8, 8.27m). “Who” finished within a tick of the demo lead in its Friday hour, while “Minute” was competitive in its bow and “Apprentice” won its second of two hours.

CW welcomed back “America’s Next Top Model” to solid scores for its 90-minute preem on Wednesday (1.6/5 in 18-49, 3.66m), but that lead-in was wasted on newbie “High Society” at 9:30 p.m. (0.5/1, 1.26m).

Primetime cable highlights included more impressive numbers for History’s “Pawn Stars” (2.5/7 in 18-49, 5.82m for its first of two segs) and “American Pickers” (1.8/5, 4.55m); the Monday combo beat NBC head to head in 18-49 from 9 to 11.

Also, E! scored Sunday with the second-season preem of “Kendra” (1.4/4 in 18-49, 2.48m), which placed second to NBC’s “The Apprentice” in its timeslot among women 18-34 (2.9/9).

Disney Channel edged past USA to lead among total viewers (2.50 million to 2.48 million), paced by the Sunday combo of “Hannah Montana” (6.92m) and “Sonny With a Chance” (5.92m) — cable’s most-watched telecasts of the week.

USA and TBS were the top cablers in demos, with the former led by “WWE Raw” and the latter by encores of “Family Guy.”