NEW YORK (Reuters) - Serbia's world number one Novak Djokovic was named Wednesday, as expected, as the top seed for the August 29-September 11 U.S. Open.

It marked the first time Djokovic was seeded number one for the year's final grand slam.

Djokovic has never won the U.S. Open but has been in great form this year, losing just two matches all season and winning the Australian Open and Wimbledon.

Defending U.S. Open champion Rafa Nadal was seeded second as tournament organizers stuck with their practice of following the official world rankings to decide the seedings.

There were two other former champions among the 32 seeds. Argentina's Juan Martin Del Potro, the 2009 winner, was listed 18th while American Andy Roddick, the 2003 victor, was seeded 21st.

(Reporting by Julian Linden; Editing by Frank Pingue)