Reigning champion Rafael Nadal pulled out of the U.S. Open because of an injury for the second time in three years Monday, leaving Novak Djokovic and Roger Federer as the men to beat at the year's last Grand Slam tournament. Nadal announced his withdrawal, blamed on a bad right wrist, one week before play begins at Flushing Meadows. "I am sure you understand that it is a very tough moment for me since it is a tournament I love and where I have great memories from fans, the night matches, so many things," a posting on Nadal's Facebook page read.