Khloe Kardashian, Tristan Thompson -- Mystery Solved in Cabo (PHOTOS)

Khloe Kardashian and Tristan Thompson have left very little to the imagination ... it's pretty clear they're hooking up.

We got this pic of the youngest Kardashian sis and the NBA champ Saturday vacationing together in Cabo ... and Tristan seems to have a good hold on Khloe.

We got them earlier this week at Bootsy's in WeHo, but they kept their distance ... leaving separately.

Nothing like a run south of the boarder to cement love.