AceShowbiz - Lady GaGa sent her entourage into panic mode at Monday, May 3 Costume Institute Gala in New York after refusing to leave her dressing room - and had to be coaxed out by the event's co-organizer Oprah Winfrey.

The "Poker Face" superstar had been personally asked by Vogue editor Anna Wintour - who throws the lavish bash at the Metropolitan Museum of Art every year - to perform for the star-studded crowd. But Gaga's team was sent into a spin when the singer reportedly locked herself in her changing area and insisted she would not walk the red carpet.

She only agreed to leave the room after TV titan Winfrey - who shared hosting duties with Wintour - encouraged her to perform, according to New York Post gossip column Page Six. An insider tells the publication, "She literally wouldn't come out. Friends tried, (Warner Music executive) Lyor Cohen tried, no dice (luck). Eventually, (artist) Vito Schnabel came over and got (GaGa's friend) Terence Koh on the phone to talk to her, which helped. Koh and Oprah were the ones who finally coaxed her out."

And the singer seemingly wasn't in the mood to stick to the rules - she told the A-list audience Wintour had requested she refrained from swearing onstage, adding: "So Anna, I will do my f**cking best!"