Kei Nishikori has insisted that he needed to fight his way to victory following a five-set battle against Milos Raonic, which took more than four hours to play.

The 24-year-old came out on top in a 4-6 7-6(4) 6-7(6) 7-5 6-4 win to grab a spot in the quarter-finals at Flushing Meadows for the first time in his career.

"It was really tight and it was really tough," Nishikori said on court after the match. "I had to concentrate against Milos, he had a great serve. I just tried to play one point at a time and keep fighting - I'm very happy to win today."

Raonic, who left the court at around 2.30am New York time, will take on Stanislas Wawrinka in the final-eight clash.