NEW YORK, United States —Ailing Novak Djokovic suffered his earliest Grand Slam exit in 20 years on Sunday, falling in five brutal sets to Mariano Navone in the first round of the US Open. The 48th-ranked Argentine’s 7-6 (7/5), 5-7, 4-6, 6-2, 6-1 victory ended Djokovic’s latest bid for a record 25th Grand Slam title.