AFP, New York :Novak Djokovic reached an eighth successive US Open semi-final, downing Andy Murray 7-6 (7/1), 6-7 (1/7), 6-2, 6-4 to set up a clash against Kei Nishikori for a place in the title match. World number one Djokovic, the 2011 champion, clinched his 50th win in New York and 13th in 21 meetings on Wednesday against his childhood rival who had taken the 2012 title. Nishikori, the 10th seed, had earlier needed more than four hours to defeat third seed Stan Wawrinka 3-6, 7-5, 7-6 (9/7), 6-7 (5/7), 6-4 to become the first Japanese man in the semi-finals in New York in 96 years.