Jimmy Fallon Debuts on Tonight Show

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Jimmy Fallon got a star-studded welcome as he took the reins of "The Tonight Show" Monday.

Robert De Niro, Lady Gaga, Sarah Jessica Parker, Mike Tyson, Joan Rivers and Joe Namath were among the celebrities who appeared as walk-ons after Fallon joked he'd made $100 bets that he'd never get the opportunity to follow in the footsteps of Johnny Carson, Conan O'Brien and Jay Leno.