If James Harden was bummed about not being in the NBA Finals ... he ain't showin' it -- 'cause he was TURNING UP with a shirtless Travis Scott onstage Saturday night!!
Just five days after being bounced from the playoffs ... the Rockets PG turned to his ex-GF's sister's BF to get away from it all ... and he got away from it.
The Beard joined Kylie Jenner's baby daddy during the last few minutes of his Governors Ball set, rockin' out to "Beibs in the Trap" .