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.
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.