Elton John and Chappell Roan turned his annual Oscars watch party into their own "Pink Pony Club" ... performing some of their biggest songs together for a good cause ... and it's all on video.

The "Rocket Man" and the "Pink Pony Club" singer collaborated Sunday night at Elton's annual Academy Awards watch party, which benefits his AIDS Foundation.

Elton and Chappell grabbed the mic and hit the stage to perform her smash hit ... with Elton belting out 'PPC' lyrics while wearing a pink cowboy hat.

Folks lucky enough to attend the party ate this all up ... check out the clips, the vibes are immaculate.

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Elton even sat down at the piano for a couple songs ... with Chappell helping him sing his 1974 hit "Don't Let the Sun Go Down on Me."

EJ shared a clip from the collab on his Instagram page and remarked, "Sharing this moment together at #EJAFOscars was nothing short of magical 💖 For one night we transformed West Hollywood Park into our own Pink Pony Club - a space filled with love and community, where everyone can be unapologetically themselves ✨."