Wednesday night might have marked [article id="1635661"]Rihanna's "American Idol" debut[/article], but the superstar delivered a fearless performance of her new single, "Rockstar 101."

"It's my first time performing on 'Idol,' and it's a little nerve-racking, because we're in the middle of our tour rehearsals and it's a really time-demanding experience, and we just had to fit this in there." she said in an interview with "Entertainment Tonight."

The songstress, who just announced her [article id="1635473"]Last Girl on Earth Tour with Ke$ha[/article] this week, confessed that her performance was completely spontaneous, revealing that she and her band "came up with what we were going to do right here, right now."

Rihanna also explained the meaning behind the title of her Last Girl on Earth Tour. "I like to think about myself as the last girl on Earth, because sometimes people make decisions based on the outlook of others and, you know, to me, my life is my life," she said. "It's my world, and I'm going to live it the way I want to. That's how I think about everything. That way I'm focused on me and my work. It's a really narrow space, a focus."

Rihanna's third Rated R single, "Rude Boy," is holding strong atop the Billboard Hot 100 for the fourth consecutive week. "It's so exciting. I can't believe 'Rude Boy,' of all songs, was the biggest song on this album, and that's the one that I really wrote the most on." she said of the song's success.

What did you think of Rihanna's "Idol" performance? Are you looking forward to her Last Girl on Earth Tour? Let us know in the comments!

Get your "Idol" fix on MTV News' [article id="1486475"]"American Idol" page[/article], where you'll find all the latest news, interviews and opinions.