“House” established more series highs Tuesday for Fox, retaining more of its “American Idol” lead-in than any show to date, according to preliminary nationals from Nielsen.

Fox looks to be unstoppable in the May sweep, which begins Thursday, as “House” (9.9 rating/24 share in adults 18-49, 24.5 million viewers overall) continues to rack up bigger numbers. Perf Tuesday repped the sixth time “House” has recorded a series high in the past three months, this time retaining a boffo 88% of its lead-in from “American Idol” (11.2/30 in 18-49, 28 million viewers overall).

This season, second-year medical drama “House” has improved upon its post-“Idol” perf from the same weeks a year ago by a big 39% in adults 18-49 (8.6/21 vs. 6.2/15) and by 38% in total viewers (21.5 million vs. 15.6 million).

In the four-week sweep period that will close out the broadcast season, Fox will air five hours of both “House” and “24” in the May sweep as well as eight hours of television’s top-rated show, “American Idol,” which itself is up about 12% vs. a year ago. These hot shows should make the net virtually impossible to beat in key demos.

Elsewhere Tuesday, CBS was again a solid — albeit distant — second to Fox with “NCIS” (3.5/9 in 18-49, 15.3 million viewers overall) and “The Unit” (3.9/9 in 18-49, 13.8 million viewers overall).

NBC was paced by a repeat “Law & Order: Special Victims Unit” (3.4/9 in 18-49, 9.1 million viewers overall), ABC by an original seg of “Boston Legal” (3.0/8 in 18-49, 9.9 million viewers overall).

Preliminary 18-49 averages for the night: Fox, 10.5/27; CBS, 3.4/9; NBC, 2.4/6; ABC, 2.2/6; WB, 1.4/4; UPN, 0.9/2.

In total viewers: Fox, 26.3 million; CBS, 13.0 million; ABC, 6.6 million; NBC, 6.1 million; WB, 3.5 million; UPN, 1.9 million.