"So this is it," Ellen DeGeneres said, staring into fellow judge Simon Cowell's eyes as they sat down for the first day of Hollywood singing on Tuesday night's (February 9) "American Idol." "I come on, you leave."

And with that, that newest member of the "Idol" panel quickly made her mark on day one of work, immediately putting to rest weeks of chatter about Cowell's imminent leave-taking at the end of this season and establishing what seems like a good-natured, jokey tension between the two new co-workers.

DeGeneres tried to put the nervous singers at ease from the moment she first stepped onstage at Los Angeles' Kodak Theater, telling the 181 wannabes, "I don't know how you feel right now. ... When people say, 'What do you know about music?' I'll tell you what I do know: I do know what it's like to stand on a stage and try to please an entire roomful of people. ... That is a hard thing to do."

Though she got to sit down while the singers took the stage, DeGeneres made her presence felt, tossing off funny asides and coherent, helpful advice while flashing just enough of her signature wit to bring a fresh feeling to the judges' panel.

"You frighten me," she told shticky singer Antonio "SkiiBoSki" Wheeler after his so-so run through "Ain't Too Proud to Beg" in one of the night's funnier moments. "You were stalking us. You were like a leopard behind a cage. ... I was watching you looking at us like, 'I'm gonna getcha.' " As the only judge to make comments, DeGeneres was firm and direct with her humorous suggestion to not frighten the audience and to remember the fine line between sexy and scary. Seemingly eager to put her "So You Think You Can Dance" guest-judging debacle behind her, DeGeneres spoke early and often, at points seemingly doing the impossible: shutting Cowell up.

She also proved that she can match the acerbic Brit with her clever put-downs, riffing in one montage, "I'm tired as it is; that almost put me right out," "It was crazy, I think, in a bad way" and reminding one contestant from Florida to wear shoes because "it's filthy here. Hollywood is a disgusting town."

At one point, after Kara DioGuardi praised Andrew Garcia's radical acoustic revamp of former judge Paula Abdul's "Straight Up," saying the onetime pop star would have loved it, DeGeneres threw her hands in the air and did a loving imitation of Abdul's signature straight-armed hand clap — erasing any doubt about whether she feels awkward taking the former judge's seat.

And when Tennessee bridge-jumper Vanessa Wolfe was clearly overtaken by nerves, DeGeneres gave her Abdul-esque, caring advice: "You're unique. I think you have a unique quality that you should embrace and just really accept who you are. You're hiding inside and just scared to death. You gotta let go of that, because those nerves are gonna kill ya." While she might have channeled Abdul for that critique, Ellen's comments were mostly an antidote to the sometimes rambling, bizarre statements Paula made during her eight seasons on the show.

It wasn't all Ellen, however, as Cowell still got in plenty of harsh digs, eviscerating a number of performers who hid behind poorly played instruments and ill-conceived song choices.

DeGeneres provided exactly what the panel lacked in the past: a strong, confident voice of reason with the right combination of humor and useful advice that could prove to be the first-ever challenge to Cowell's domination of the critiques. "You have an amazing voice and you were very in that song," she told mom rocker Mary Powers after a rough-and-tumble cover of Pink's "Sober."

With tensions running high at one point, she played around with one group, telling them to step up, back, to the side and then up again before putting them all through to the next round to loud applause and laughs.

Speaking to host Ryan Seacrest backstage at the top of the show, DeGeneres set the tone for what her likely contribution to the show will be: arch but broad humor. "There's been a lot said about what kind of judge you will be on the show," Seacrest said. "Kind, generous, honest, but at the same time pretty direct. And one of the few people I think that can be honest with Simon about how he takes on the contestants. Is that your plan?"

Without missing a beat, DeGeneres shot back, "I'm sorry, I wasn't listening."

How do you think Ellen did on her first "Idol" night? Sound off below!

Get your "Idol" fix on MTV News' "American Idol" page, where you'll find all the latest news, interviews and opinions.