NEW YORK (AP) — Novak Djokovic has picked up his 17th consecutive victory over Kei Nishikori to reach the fourth round at the U.S. Open as he pursues a calendar-year Grand Slam. The top-seeded Djokovic dropped the opening set before coming back to win 6-7 (4), 6-3, 6-3, 6-2 in Arthur Ashe Stadium on Saturday. Djokovic needs four more wins next week to become the first man since Rod Laver in 1969 to win all four major tennis championships in one season. He also can claim a 21st Grand Slam title to break the career mark for me he shares with Roger Federer and Rafael Nadal. Other winners Saturday include Bianca Andreescu and Belinda Bencic.