Boy, they really mixed it up during disco night on "American Idol" last night, and in the process it quickly became clear who is the lightweight in this show.

That would be Randy Jackson.

Until now, Jackson had been the first to comment on the performances he and fellow judges Paula Abdul and Simon Cowell saw each week. Simon always went last. Randy never made any sense when he critiqued a contestant, saying things like "it wasn't, like, there for me, you know?" We thought it was just his way of expressing himself. But last night host Ryan Seacrest announced, to the surprise of the judges, that Simon would go first and Randy last. Randy spoke standard English for the first time, but he also repeated whatever Simon said. Eventually, Randy felt compelled to comment on the fact that he was doing that, feigning bewilderment and suggesting that it must be something in the water. Yeah, that's it, the water.

With Simon instead of Randy as her lead, even Paula began offering genuine criticism of the performances. Ditto guest judge Donna Summer who was much less effusive than previous guest judges. So stunning was the turnaround that contestant Jasmine Trias was reduced to tears when even Paula couldn't find nice things to say about her second song of the night.

Only once did Randy veer from Simon's script: After Diana DeGarmo sang her first disco number, he started nicking Simon for having said weeks ago that she was too young for the competition. Of course, Randy's observation came after Simon himself had just reminded viewers that he had once made that comment, noted he'd been wrong and taken it back.

"Shut up, Randy, you're boring," Simon snapped as Randy got rolling, which was true enough.

Oh yes, and the four remaining contestants sang disco songs with varying degrees of success. Jasmine hit a couple of notes. Fantasia Barrino and La Toya London continued to deliver terrific performances, though their song choices were a bit dicey and, it turns out, La Toya really does lack the gene for personality. Diana came on strong with her second song of the night but continues, with her blond flippy hair, zaftig figure and grating personality, to channel Miss Piggy, which could be a problem in a pop star.