Tuesday's viewership of 29.9 million is about 2 percent lower than last year's season debut audience of slightly more than 30 million, according to preliminary Nielsen Co. figures released Wednesday.
By comparison, the 2009 debut episode saw a 10 percent drop compared to 2008.
It's an indication that "Idol" can capitalize on cast changes like Abdul's to resist potential viewer boredom as it ages. That will be further tested when judge Simon Cowell leaves after this season to launch another Fox talent contest, "The X Factor," next year.
The 37.4 million who watched the 2007 debut represent the series' high point for opening nights.
"I think people love to love the show," said Mike Darnell, Fox's executive in charge of alternative programming. "It's one of the few phenomena that exist: the Super Bowl, the Oscars, `American Idol.' It's an American tradition.'
The tradition began in Britain as "Pop Idol," which was created by entertainment mogul Simon Fuller and whose 19 Entertainment carried the concept to more than three-dozen TV markets worldwide. FremantleMedia North America teams with 19 Entertainment, a division of CKX Inc., in producing the U.S. version.
"What we've proved now, again, not that we need to prove anything, is this show is about the public's relationship with the fundamental things in life," said Fuller, calling "American Idol" "authentic" in its celebration of people's dreams and aspirations.
Fans can accept change, he added: Who would have thought the James Bond movies would have become such a remarkable franchise over the years "with so many Bonds."
"American Idol" has been the top-rated show for five years among all viewers and for six years among the advertiser-favored 18 to 49 audience.
Abdul, who had been with the show since it started, left over a salary dispute. Her place is being filled first by celebrity panelists, including Victoria Beckham and Katy Perry, and later this season by new judge Ellen DeGeneres.
Fuller said he was unconcerned that "The X Factor," based on Cowell's hit British series of the same name, might affect the audience for "American Idol" by diluting the talent-show marketplace. If it's an issue at all, he said, it's one that's more than a year away.
"That's not my worry. ... We're the biggest talent show on earth. All I'm really worried about is `Idol,' and we're strong," he said, adding, "America has such an incredible talent pool."
"The X Factor," with Cowell as judge and executive producer, will air in fall 2011, with "American Idol" keeping its January to May run.
Another top TV competitor, CBS' "NCIS," held its own against the Fox series with an audience of nearly 21 million, just shy of its pre-"Idol" performance. The drama has been the season's top-ranked series so far.
By LYNN ELBER