Last summer Fox rolled out its big-buzz new series “Prison Break” weeks ahead of the other broadcast networks’ offerings, and to good effect: It averaged an impressive 4.6 adults 18-49 rating in its debut.

Last night the network attempted the same strategy with one this fall’s biggest-buzz new shows, the kidnapping drama “Vanished.” The result was disappointing.

Against mostly repeats, “Vanished” averaged a 3.0 adults 18-49 overnight rating, ranking No. 1 in its timeslot but losing 19 percent of the audience of lead-in “Break,” which averaged a decent 3.7 in its second-season debut.

Perhaps more troubling for Fox, “Vanished” slipped 6 percent from its first half hour to its second, from a 3.1 to a 2.9, and was just 0.2 ahead of a rerun of “Wife Swap” on ABC in its 9 p.m. timeslot.

Though the show got strong web buzz, ranking as the No. 3 most-talked-about new show on online forums, messageboards and blogs, according to Interpublic’s recent PropheSEE report, critics did not find the show as interesting. It got mostly poor reviews.

“It’s pretty mediocre television, having the feel of a cut and paste job, without one thing that ties a successful series together as a unique creative experience,” wrote Andrew Lyons, in a Media Life review.

“Vanished” may also have suffered from the very strategy that helped last year, the early debut. Viewers don’t expect the TV season to kick off so early. Plus, it aired opposite the surprisingly solid season and presumably series finale of NBC’s “Treasure Hunters,” which averaged a 2.5, its best rating in eight weeks and up 39 percent over its penultimate episode last week.

The slate of new shows led Fox to No. 1 for the night among 18-49s with a 3.3 rating and 10 share, trailed by CBS at 2.7/8, ABC at 2.3/7, NBC and Univision both at 1.8/5, and WB and UPN each at 0.7/2.

At 8 p.m., Fox was No. 1 at 3.7 for "Prison," ahead of ABC's "Swap" rerun at 2.3, CBS's repeats of "Two and a Half Men" and "How I Met Your Mother" at 2.2, Univision's "La Fea Mas Bella" at 1.8, NBC's "Hunters" at 1.6, WB's "7th Heaven" repeat at 0.7 and UPN's repeats of "One on One" and "All of Us" at 0.6.

At 9 p.m., Fox led again at 3.0 for "Vanished," followed by ABC's "Swap" rerun at 2.8, CBS's "Men" and "New Adventures of Old Christine" repeats at 2.7, NBC's "Hunters" at 2.5, Univision's "Barrera de Amor" at 1.5, and UPN's reruns of "Girlfriends" and "Half & Half" and WB's "Heaven" repeat each at 0.7.

At 10 p.m., CBS led at 3.3 for a "CSI: Miami" repeat, ahead of ABC at 1.9 for a "Supernanny" rerun, NBC at 1.5 for a "Medium" repeat, and Univision at 2.0 for "Cristina."

Among households, CBS was No. 1 for the evening with a 6.1 rating and 10 share, edging Fox at 5.7/9. ABC was No. 3 at 4.1/7, followed by NBC at 3.2/5, Univision at 2.1/3, WB at 1.2/2 and UPN at 1.1/2.