Hot idea with much sensuous detail. It's a good attempt, would be more effective if the text were split up a bit and maybe explained how the subject landed in this situation. Has he actually sworn some sort of oath to Ms Sharapova? Is it a wager?

It would serve the story, too, if you indicated by some detail early on whether the narrator is a man or a woman; we don't find that out for sure until the cock is mentioned. I figured it was likely a guy, but of course lesbians get off on female tennis stars too. Good luck, and I hope to read more from you!