Jay-Z Performs 'Watch The Throne' Track at 'Harder They Fall' Screening

Jay-Z must have been feeling it after showing off his new movie, because he hopped on the mic and threw down ... on a classic track he did with Kanye.

The hip-hop mogul put on an apparently impromptu show Wednesday night at L.A.'s Shrine Auditorium following a screening of "The Harder They Fall" ... a Western with a mostly Black cast that he produced.

Jay held a celebration event after the film, and gave a rare live performance with the band ... spitting some lyrics from "Gotta Have It," from his 2011 collab album "Watch the Throne" with Ye.

It's just another sign things are cool again between the legendary rappers ... on the heels of Jay surprisingly featuring on "Jail" from West's "Donda" album.

"The Harder They Fall" party only kept elevating, as Seal also joined the band and showed off his pipes ... and everyone appeared to be loving it.

Some of the other celebs in attendance included Regina King -- who stars in the movie -- Tiffany Haddish and Swizz Beatz.