Lady Gaga Does Surprise Performance Of 'Shallow' With U2 At Las Vegas Sphere

Lady Gaga just made her own special debut at the Sphere in Las Vegas ... performing her hit track from "A Star Is Born" during a surprise appearance at U2's show.

The singer joined Bono and co. at the one-of-a-kind venue Wednesday night to sing "Shallow" -- a true treat for the massive crowd.

Those in the audience even joined in, with LG and Bono giving the crowd a chance to belt out the chorus for the Oscar-winning track.

That's not all, though -- Gaga also performed with U2 for the band's 1988 song, "All I Want Is You" ... making fans go nuts once again.

This ain't the first time the 2 forces of music teamed up, BTW ... you'll recall, she made a surprise appearance in 2015 during U2's "Innocence + Experience Tour," jamming out to "Ordinary Love."

Gaga's recent Sphere pop-in comes on the heels of her jumping on stage with the Rolling Stones in New York last week ... not to mention her brief appearance on Bad Bunny's episode of "Saturday Night Live."