UPDATE: Fox has released time-adjusted fast nationals for American Idol, which was adjusted up to a 7.4 rating in 18-49 and 21.9 million viewers, bringing the year-to-year drops to 24% and 17%, respectively.

PREVIOUS: Eleven seasons in, American Idol is starting to come down to earth. Last night’s Season 11 premiere of Fox’s ratings juggernaut drew 21.6 million viewers and a 7.2/18 among adults 18-49. That was down 26% in the 18-49 demo and 18% in viewers from last year’s premiere (fast nationals-to-fast nationals) and the reality veteran’s lowest-rated season opener since the show’s inauspicious debut in summer 2002 (see historical data below). It also represents Idol’s biggest ratings drop between seasons. Last season’s premiere, also at the time the lowest-rated since Season 1, posted the second-biggest drops of 12% (viewers) and 17% (adults 18-49). A lot has changed since the show’s 10th season opener in January 2011. Back then, Idol was the only game in town in terms of big-scale singing competitions. Since then, two formidable rivals have entered the fray: NBC’s The Voice and Fox’s The X Factor, crowding the space.

Even at those levels, Idol is by far the highest-rated entertainment program on TV. It almost doubled the premiere ratings for X Factor and dominated primetime last night. As expected, the biggest casualties were the most vulnerable — in this case NBC’s fledgling 8 PM comedy block. Whitney (1.6/5) was down 20% from last week’s time-slot premiere to a series low. In its second airing, Are You There, Chelsea (1.8/4) was down 22% from its debut. NBC’s older skewing Harry’s Law (1.1/3) weathered the storm better, down 8%, while Law & Order: SVU (1.8/5) at 10 PM was down 10% for a series low even without Idol competition.

ABC’s 8-9 PM comedies also took a hit against Idol. The Middle (2.6/7) and Suburgatory (2.5/6) were down 10% and 14%, respectively, from last week to hit season lows. Modern Family (5.0/12) and Happy Endings (2.9/7) came out largely unscathed. Modern Family‘s much-talked-about “Lily says the F-word” episode was down a tenth from last week, as was Happy Endings. This was Modern Family‘s best-ever result against Idol, up 9% from last year. The network’s soap Revenge (2.5/6) was the only program last night to post ratings gains, up 4% from last week. Following an NCIS repeat, CBS’ Criminal Minds (3.2/8) was down 6% from its last original five weeks ago, and CSI (2.8/7) was down a tenth.

Here is historical data for the American Idol season premieres (this year’s ratings are fast nationals, all others are Live+Same Day):

1/18/12 21.6 million 7.2/18 in adults 18-49

1/19/11 26.3 million 9.8/26

1/12/10 29.95 million 11.8/29

1/13/09 30.45 million 11.7/28

1/15/08 33.48 million 13.8/32

1/16/07 37.44 million 15.8/36

1/17/06 35.53 million 15.3/34

1/18/05 33.58 million 14.0/33

1/19/04 28.96 million 12.9/30

1/21/03 26.50 million  12.4/30

6/11/02 9.85 million 4.8/14