Fallon, 42, reminded Hudgens, 28, of the network's past comedies — Seinfeld and Cheers — before they made their way to center stage to belt out the Friends theme song.
The Powerless actress, 28, and Fallon received a loud round of applause with their impressive ballad version of The Rembrandts' 1995 hit "I'll Be There for You."
Hudgens, of course, is used to singing on camera. The former Disney star has shown her range in the High School Musical franchise and she played Betty Rizzo in the Fox smash production of Grease: Live last January.
Hudgens and Fallon may love the tune, but the Friends cast hated it. "We were all never a big fan. No one was really a big fan of that theme song," Jennifer Aniston, who played Rachel Green, said during BBC's The One Show in November.
"I'm sorry. I don't mean to say that. We felt it was a little …. Dancing in a pond, like a fountain? It felt sort of odd," she said, referring to the show's opening iconic credits. "But we did it, because we were told to."
Watch Hudgens and Fallon in the video above!
Sign up now for the Us Weekly newsletter to get breaking celebrity news, hot pics and more delivered straight to your inbox!