Maria Sharapova Serena Williams are at the top of the rankings 2011

While neither Maria Sharapova or Serena Williams are at the top of the rankings, they both are dangerous competitors on hard courts. Source: Reuters / Vostock Photo When the U.S. Open begins in Flushing Meadows, New York, on Aug. 29, all eyes will be on Maria Sharapova and Serena Williams. Both are accomplished hard court players, and they are likely to be tough competitors in this