The 128th U.S. Open begins Monday, Aug. 31, 2009. Like the defending champions before them, Roger Federer and Serena Williams hope to defend their turf. However, history shows it can be difficult to do.
The underdogs are always lurking just around the corner seeking their defining moment. Let's take a look back at some of the tournament's greatest upsets, when the hopes of champions were crumbled.