Metta World Peace -- SAVED BY GHOST DJ ... at Vegas Nightclub

There was a g-g-g-ghost at Metta World Peace's "Celebrity DJ" gig in Vegas this weekend -- a virtually invisible woman haunting the booth ... and saving Metta's ass from utter embarrassment, TMZ Sports has learned.

Peace was all set up to control the turntables at Chateau nightclub Saturday night -- but the problem is, he's not experienced/good enough to be out there all by himself.

Sooooo ... our sources tell us Metta was accompanied by a "ghost DJ" -- a woman named Catherine Ouellette ... who kept the ship afloat while Mr. Peace grabbed the mic and kept the crowd fired up.

Smart move ... you wouldn't jump out of a plane without a parachute, would you?

(OK, maybe if you're Travis Pastrana ... seriously, you need to watch this clip)