Tennis-Djokovic-Federer final begins after 3-hour delay

(Updates with start of play at U.S. Open) NEW YORK, Sept 13 (Reuters) - The U.S. Open men's final between top seed Novak Djokovic and second seed Roger Federer began three hours after the originally scheduled start due to rain at the U.S. National Tennis Center on Sunday. Skies darkened and winds picked up just before the players were scheduled to take the court for warm-ups at 4 p.m. ET (2000 GMT) and the start was then delayed after rain began to fall. With the blue court dried and the storm system gone from the area, the players finally came out at 7:10 p.m. ET to warm up at Arthur Ashe Stadium, where the shell of a retractable roof is in place and expected to be in operation for next year's U.S. Open. World number one Djokovic, 28, is seeking to win his third grand slam crown of the year after winning the Australian Open and Wimbledon titles. Federer, 34, is aiming to add to his all-time record 17 grand slam singles titles and first since his 2012 Wimbledon triumph. (Reporting by Larry Fine; Editing by Frank Pingue)