• by Wayne Friedman , January 18, 2007

For its sixth season debut, Fox's industry-leading "American Idol" hit even more viewership records Tuesday night. But if there is one minor chink in the show's almighty armor, it is that its growth rate appears to be slowing down.

"Idol" grew 3% to a 15.7 adults 18-49 rating, according to Nielsen preliminary ratings--the best season debut yet. This was against last season's debut of 15.2.

In addition, the debut was the series' second-highest ratings ever, lagging only behind the second season finale of "American Idol" in 2003. Total viewers climbed 4% to 37 million, up from 35.5 million of a year ago.

"Idol" couldn't match the 10% or 15% increases in ratings versus other recent season debuts, but analysts still count the 2007 opener as a triumph for the No 1-rated network prime-time series.

"The fact that it is even up even minimally is an achievement in this environment," says Brad Adgate, senior vice president and corporate research director for Horizon Media.

Analysts have been astounded by the growth of the show in recent years--and particularly dumbfounded that it has defied the normal broadcast ratings program trajectory for a 6-year-old show.

By way of comparison, some top net shows younger than "Idol" have actually dipped in household fourth-quarter ratings. Adgate notes that "Desperate Housewives" dropped 14%; "CSI" was down 27%; "Lost" slipped 10%; and "Without a Trace (in a new time period) sank 26%.

While most networks shied away from the "Idol" juggernaut on the night, others pulled in decent performances. CBS' drama "NCIS," which ran against the first hour of "Idol" from 8-9 p.m., drew a decent 3.8 18-49 rating, finishing second in the time period. At 9 p.m., "The Unit" grabbed a 3.1 rating among 18-49 viewers.

After the "Idol" two-hour premiere ended, NBC picked up the pieces with "Law & Order: Special Victims Unit," which grabbed a 4.7 rating among 18-49 viewers.

"Idol's" huge night led Fox to an easy first-place finish for the night among 18-49s with a 15.7 rating/36 share. CBS was next at 3.2/8; NBC was third at 2.9/7; then ABC, at 2.1/5; Univision was fifth at 1.8/4, and CW was sixth at 0.6/1.