Jimmy Fallon as Tonight Show Host: Grade Him!

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I'll be your host ... for now.

So opened Jimmy Fallon as host of The Tonight Show on Monday, as the former SNL cast member took over for Jay Leno and welcomed a star-studded lineup on his first night.

Robert DeNiro cam out to pay up on a $100 bet during the monologue - and that was just the beginning.

Others who stopped by included Tina Fey, Kim Kardashian, Lady Gaga, Sarah Jessica Parker, Seth Rogan, Lindsay Lohan, Mariah Carey, Joan Rivers, Tracey Morgan and Mike Tyson.

Will Smith was the first official guest, pre-taping a segment titled "The Evolution of Hip-Hop Dancing" and then talking about such topics as skydiving and snowboarding.

U2 played as the musical guest and, overall, Fallon came across as both nervous and sincere.

"I just want to do well," Fallon told the audience . "If you guys let me stick around long enough, maybe I'll get the hang of it."

What did you think of Fallon's debut? Grade it now:

Matt Richenthal is the Editor in Chief of TV Fanatic. Follow him on Twitter and on Google+.

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