Lady Gaga and Bradley Cooper performed the duet from their recent film live for the first time Saturday night. "Bradley, thank you", said Gaga, with Cooper then tossing his baseball cap into the audience.
"I even got you in-ears", Gaga told Cooper after the two embraced, describing the earphone-like monitors used onstage.
Gaga kneeled on the ground beside Cooper, who sat on a stool for the song and looked down at her warmly, resting a hand on her arm as he sang.
Bradley Cooper directs and stars in A Star Is Born alongside Lady Gaga.
The song, which was nominated for an Academy Award earlier this week, is the closing number of the "Enigma" show, the residency that kicked off in late December.
The crowd reportedly cheered as Cooper made his way to the stage.
The single won a Golden Globe for Best Original Song and was nominated for an Oscar for Best Original Song as well as for four Grammys, including Record of the Year and Song of the Year. After Gaga sang her verse, the stars joined each other for a powerful chorus, likely not leaving a dry tear in the room.