Serena Williams is the top seed at the U.S. Open and the defending champion. But she comes to the final Major event of 2014 trying to salvage a disappointing season, at least by her standards. While Serena has won five titles on the WTA Tour and hung on to her top ranking this year, she has yet to advance to the second week at the first three Majors. Why? Consider her serve and return percentages in her Slam losses versus her tournament play and, well, it becomes clear what she’ll need to improve if she has designs of remaining the queen of Queens.