Nadal pulls out of US Open

Federer and Djokovic now front-runners for the title at last major of year

Reigning champion Rafael Nadal pulled out of the US Open because of an injury for the second time in three years on Monday, leaving Novak Djokovic and Roger Federer as the men to beat at the year's final Grand Slam tournament.

Nadal announced his withdrawal, blamed on a bad right wrist, one week before play begins at Flushing Meadows.