Jimmy Kimmel Jimmy Kimmel

In a vicious sendup, Jimmy Kimmel impersonated Jay Leno — complete with gray wig, fake lantern chin and a slight lisp — as he did his monologue, and he stayed in character throughout the program.

VIDEO: Watch Kimmel's entrance and monologue as Leno now

"Hello, hello, my name is Jay Leno ... and I'm taking over all the shows in late night," began the host of ABC's Jimmy Kimmel Live! in his new persona.

"It's great to be here on ABC," he said, exaggeratedly playing off his bandleader (Cleto Escobedo III) like Leno. "You know what ABC stands for? Always Bump Conan.

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"Anyway, Conan O'Brien today announced that he is leaving NBC. He released a statement today that said I won't participate in the destruction of The Tonight Show. Fortunately, though, I will.

"Those of you who tuned in to see Jimmy Kimmel tonight, he's gone. Jimmy's not here anymore. Don't worry. He'll be fine. He picked up an endorsement deal from Jenny Craig."

Kimmel moved on to other topics, all in his Leno alter ego.

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His mannerisms constituted a mocking parody of Leno, looking for help for punch lines that bombed from the band, which punctuated his jokes with a little rim shot or riff.

And when the one-liners really crashed, Kimmel's Leno said, "You know, on my show, everyone applauds after every joke."

It was as if Kimmel were trying to make the jokes as painful and predictable as possible — mimicking Leno's propensity to drive home a joke's payoff.

Letterman's monologue: "I knocked off another competitor"

"You hear about this? Baseball slugger Mark McGwire admitted to using steroids. He came clean on the popular show No! Duh! with Bob Costas. You may remember four-and-a-half years ago, Mark McGwire testified before Congress. Remember that? He wasn't completely honest. He said, 'I picked up the syringe, but I did not impale. Did not impale.'"

 He kept up the assault, doing a "Headlines" bit à la Leno.

His first guest, Chevy Chase, played along — not totally comfortably — commenting on never knowing that Leno had trouble with his "T-Hs."