One of Tiger Woods' alleged mistresses was already bragging about hooking up with the golfer way before Tiger crashed his SUV into that tree -- and the admission was all caught on tape.

Porn star Holly Sampson -- alleged mistress #79 -- talked openly about allegedly bedding Tiger Woods on an adult website called Naughty America back in May.

Nobody believed it back then -- but that was before Tiger admitted his "transgressions."

Thanks to sportsbybrooks.com for calling this one out.