Video shot by audience members showed Gaga inviting Cooper, who also directed the film, onstage for the performance. She's performed the song solo as the encore of "Enigma," her Las Vegas residency, since it opened in December, according to Billboard, but this was their first live performance together.
"Star" is up for more than a dozen Oscars, including best picture, best actress, best actor and best adapted screenplay. The film also received SAG, Golden Globe, Critics' Choice and Grammy nods.
Click here for the full list of Oscar nominees.