While the other networks have slipped into March rerun mode, Fox is on a hot streak that has seen it move into a tie with CBS for first place for the season among adults 18-49. Last week the network had seven top 10 shows among 18-49s for the first time since 1991.

And last night, it obliterated the rerun-heavy Big Four networks with a two-hour edition of “American Idol.”

“Idol” averaged an 11.5 18-49 rating, according to Nielsen overnights. That was well ahead of the 7.1 combined rating averaged by ABC, CBS, NBC and the CW, which had only three original episodes between them during “Idol’s” 8 to 10 p.m. block.

It also finished some 5 million ahead of the Big Four combined among total viewers, averaging 29.4 million total viewers.

It’s worth noting that “Idol’s” rating was actually down 15 percent from the same night last year in 18-49s, when the show averaged a 13.5. But it seems there’s a cause for that: the start of daylight savings time three weeks earlier than usual and unseasonably warm weather on the East Coast, which drew many people away from their television sets.

Fox points out that there was a 12 percent decrease in persons using television among 18-49s last night compared with the same night the year before. The networks also saw a decline in PUT levels on Monday night, too, a trend that bears watching.

The network also points out that last night’s supersized episode, which combined the male and female finalists for the first time, was up 5 percent over last week’s Tuesday show to a 10.9.

Fox finished the night with an 11.5 average rating and a 31 share. CBS was second at 2.5/7, NBC third at 2.1/6, Univision fourth at 1.7/5, ABC fifth at 1.6/4 and CW sixth at 0.9/3.
 
At 8 p.m. Fox led with a 10.5 rating for its first hour of “Idol,” followed by a 2.5 for CBS for a repeat of “NCIS” and a 2.0 for NBC for “Dateline.” Univision was fourth that hour with a 1.8 for “La Fea Mas Bella,” ABC fifth with a 1.5 for a repeat of “America’s Funniest Home Videos” and CW sixth with a 0.8 for a “Gilmore Girls” rerun.
 
Fox extended its lead at 9 p.m. as “Idol” grew to a 12.4, with CBS a distant second with a 2.0 for a repeat of “The Unit.” Univision and ABC tied for third at 1.8, Univision for “Mundo de Fieras” and ABC for “Primetime,” with NBC fifth with a 1.7 for a repeat of “Law & Order: Criminal Intent” and CW sixth with a 1.1 for “Pussycat Dolls Present: Search for the Next Doll.” That show declined in virtually every demographic from last week, when it did not face “Idol.” But it did show growth from its lead-in and ranked second in the timeslot among 18-34s.
 
CBS finished first in the rerun-filled 10 p.m. hour, leading with a 2.9 for a repeat of “CSI.” NBC was second with a 2.5 for a repeat of “Law & Order: SVU,” Univision fourth with a 1.5 for “Ver para Creer” and ABC fourth with a 1.4 for a “Boston Legal” rerun.
 
Fox also nearly eclipsed the rest of the networks combined for the night among households, finishing first comfortably with a 17.0 average rating and a 27 share. CBS was second at 6.2/10, NBC third at 4.8/8, ABC fourth at 3.7/6, Univision fifth at 2.1/3 and CW sixth at 1.5/2.