Duke Porn Star Belle Knox -- BUMMED OVER NCAA UPSET

Duke's shocking 1st round upset in the NCAA tournament today really hit hard with Duke porn star Belle Knox ... who tells TMZ Sports she wants to comfort her team ... with her vagina.

As we previously reported, Knox offered the Blue Devils free sex toys from her sex toy line if they won the tourney -- including one item that happens to be a mold of her crotch.

But after Duke was knocked out by Mercer ... Knox says she still bleeds blue and white -- saying, "They played hard and I love them ... of course, I'll give them [my sex toys] for free."