Jimmy Iovine & Liberty Ross: Score Lady Gaga as Wedding Singer

Jimmy Iovine and Liberty Ross celebrated their wedding Sunday night with an insane celebrity guest list ... and perhaps the all-time greatest wedding band performances.

The party went down at David Geffen's Beverly Hills mansion and since Iovine is the co-founder of Interscope Records, the talent was ridiculous -- we're told Mary J. Blige and Swizz Beatz performed. But the main event was Lady Gaga and Tony Bennett's duet on the jazz classic, "It Don't Mean a Thing."

The Valentine's night event was packed with A-list couples such as Oprah and Stedman, Ellen and Portia, Tom Hanks and Rita and Pharrell and Helen Williams. All guests were asked to wear red for the occasion.

No traditional first dance for Jimmy and Liberty ... who instead opted to share the floor with their guests late into the night.

They officially tied the knot with a beach wedding on Saturday.