There was no hair-pulling between Mariah Carey and Nicki Minaj on the season debut of American Idol, although some viewers may have been reduced to it.

The pop divas exchanged insults worthy of teenagers, fellow judge Keith Urban looked trapped between them, and there was a whiff of make-believe about the show's touted feud.

"We can have accessories. I didn't know that was allowed. That's all I'm gonna say," Mariah commented archly about Nicki's flashy, drum major-style hat.

The rapper took offence.

"Why'd you have to reference my hat?" she said. Mariah then accused Nicki of rudeness to her during an earlier elevator meeting.

Mercifully, a contestant arrived to break up the bickering.

Whether the clash is real or not, Nicki's scrappiness came off as far more entertaining than Mariah's demure, even queenly manner.

The award for least self-absorbed judge goes to genial country singer Keith.

The two-hour episode opened by showcasing last year's winner, Phillip Phillips, and those alumni with established careers, including Carrie Underwood, Kelly Clarkson and Jennifer Hudson.

Idol, hosted by Ryan Seacrest, lost its status as the most-watched TV programme for the first time since 2003, eclipsed by NBC's Sunday Night Football, and pegged its lowest-rated season since it debuted in summer 2002.