By James Hibberd
Updated January 26, 2012 at 08:29 PM EST
American Idol 11
Credit: Fox

After eight seasons at No. 1, American Idol could finally get overthrown in the weekly ratings as the country’s highest-rated entertainment series.

The media often speculates about such a prospect before a new season of Idol premieres. Then the reality titan always returns to monster viewership, crushing all rivals in its path, and doubters are silenced.

Not this time.

The first three episodes of the 11th season, while still ruling their respective evenings, dipped far enough in the ratings to suggest that Idol could possibly get overtaken — at least during some of the upcoming weeks (overturning Idol as the season’s overall highest-rated show remains unlikely). Last Thursday’s second episode had CBS declaring an unprecedented ratings victory for its hit comedy Big Bang Theory, saying the show actually beat Idol in the key adult demo. Who actually won the fight is a matter of dispute (Fox compared Big Bang to Idol‘s hour-long average; CBS compared Big Bang to the first half of Idol, when the sitcom and reality series were in direct competition).

Either way, the point remains: The Idol pinata is within striking distance.

Though Idol continues to deliver huge numbers, here’s why the ratings suggest that regime change is theoretically possible: Idol ratings tend to follow a similar pattern every year, with very strong opening weeks, some sagging during the middle, then rising again for a big finish. The pattern has been so consistent that Fox insiders can generally predict Idol‘s ratings for its entire season based on the first few weeks. Whereas comedies like Big Bang tend to be relatively stable during their run. So if the standard Idol trend holds, given where the show is right now, things could get intensely competitive in the coming months.

“It’s still a really strong show, it’s just not quite the Death Star anymore,” said a rival network’s executive. “From a competitive standpoint, its a good thing to see it back down to Earth.'”

Which show has the best odds of taking Idol‘s place in the weekly top spot?

Big Bang or ABC’s Modern Family have the strongest claim in the demo, with an edge to Big Bang (Wednesday’s Modern Family is higher rated overall this season, but Idol is generally more vulnerable on Thursdays).

And then there’s The Voice. The second season return of NBC’s breakout hit is a wild card this season, with its season premiere fueled by the Super Bowl on Feb. 5. Though unlikely to topple Idol, here’s the key question: Will The Voice steal some thunder from Idol, or does Idol‘s dip suggest viewers are suffering singing-show fatigue in general? Between Idol, Fox’s The X Factor, NBC’s The Voice, Sing Off and America’s Got Talent, there are singing competition shows year around, more than ever before.

Fox didn’t have much of a choice about picking up X Factor, which aired this fall to solid ratings and will return next fall (you either keep Simon Cowell on your payroll or watch him stroll over to a rival). But industry insiders believe Factor is likely at least part of the reason why Idol‘s recent premiere was lower than expected. And all the other shows can’t help either.

One thing to remember is that Idol‘s run continues to be remarkable. The show ended its 10th season at No. 1 last year, and the last show to pull that off was NBC’s Cheers. Plus, Idol accounts for 50 hours of Fox’s annual programming while Modern Family and Big Bang are on the air for only about 11 hours.

As one rival put it: “No one is dancing around singing ‘Ding Dong the Witch is Dead.'”

Read more: