And finally tonight, a kid finally gets to be on the same playing field as her idol. But at the end of the match, the idol has fallen. A young american athlete is celea victory tonight, with wonder and also a few tears. Abc's ron claiborne on the new cinderella. Reporter: Call it the "shock heard round the tennis world." 19-year-old sloane stephens taking out one of the greatest players ever to lace on a pair of tennis shoes. Talk about david versus goliath. Sloane had never before reached a grand slam semifinal. Serena williams holds 15 grand slam titles. And she was sloane's childhood idol. She had her poster on her bedroom wall. This morning when I got up, i was like, "look, dude, you can do this. Just go out and play and do your best. Reporter: Sloane first picked up a racquet at the age of 8. She's the daughter of two gifted athletes. Her father, a formers pro football player who died in a car accident four years ago, her mother sybil, a swimming star at boston university. This is probably the first time sloane's gone into a season saying, "i can't wait to get out there and play." Reporter: Sloane's big breakthrough year in the french open and wimbledon, and on the pages of "vogue" magazine, which named her one of its up and coming "style stars." And yesterday, it was her style on the tennis court that drove serena williams to frustration. Now having conquered her one time idol, sloane now has somewhat of a new perspective. This is so crazy, but -- oh, my goodness. I think I'll put a poster of myself now. Reporter: Ron claiborne, abc news, new york.