Video shot by audience members showed Gaga inviting her "A Star is Born" co-star Cooper, who also directed the film, onstage for the performance of "Shallow."
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.
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