Summary: James Waterson reports on day four from the US Open. Roger Federer and Serena Williams secured easy victories, and they were joined by Tomas Berdych, Kevin Anderson, Andrea Petkovic and Francesca Schiavone in the third round. Sloane Stephens upset 23rd-seeded Shahar Peer in straight sets, and Vania King also scored a win of her own. Finally, Tommy Haas said today he considered changing his country of representation to the United States, but said he was too busy to make the phone call to the ATP.
