Kei Nishikori stunned Andy Murray to reach the US Open semi-finals, holding his nerve in a gripping final set to move two wins away from becoming the first Asian man to capture a Grand Slam singles title. Japanese star Nishikori clinched a dramatic 1-6, 6-4, 4-6, 6-1, 7-5 comeback triumph in a shade under four hours against the Wimbledon and Olympics winner and 2012 US Open champion. In Friday's semi-final, the 26-year-old will take on Swiss third seed Stan Wawrinka who defeated tearful Juan Martin del Potro, the 2009 champion, 7-6 (7/5), 4-6, 6-3, 6-2. Wawrinka, who had to save a match point in his third round clash with Dan Evans, will be playing in a third US Open semi-final in four years. The other semi-final on Friday will see defending champion Novak Djokovic take on 10th seeded Frenchman Gael Monfils. "It was one of my toughest matches mentally and physically. Juan Martin's an incredible player," said Wawrinka. "I tried to make longer rallies. I tried to go back a little bit to make him play more balls, keep him on the backhand side and tried to dictate." In a match which featured 17 breaks of serve, Nishikori prevailed for only his second win in nine matches against world number two Murray. His win came just three weeks after losing to Murray in the Olympic semi-finals. "It was a really difficult match. I didn't start well. I felt it was really quick and I was missing too much," said Nishikori after reaching only his second Slam semi-final after his runner-up spot in New York in 2014. "In the fourth and fifth sets I think I played some of the best tennis."