Kei Nishikori was proud of his grittiness and felt a rain delay helped him overcome Andy Murray in the US Open quarterfinals.

Read:>Kei Nishikori stuns Andy Murray at US Open

The Japanese sixth seed came away a 1-6, 6-4, 4-6, 6-1, 7-5 winner over World No. 2 Murray at Arthur Ashe Stadium on Wednesday.

Also read:>Murray rues serving display in US Open loss

Nishikori said a rain delay during the second set aided him, having made 14 unforced errors to drop the first in 35 minutes.

"It was a really difficult match. I didn't quite start well and lost 6-1. I felt it was really quick and I was rushing a little bit and missing too much unforced errors," he said.

"But after the rain delay I think I improved little bit with my coach, and I tried to change a little bit my tennis and it started working a little bit better. I started to get my rhythm back. Yeah, many breaks today. Especially fifth set it was really tough. I was up 4-3, 40-0 and lost the game.

"So there was many up and downs, but I tried to stay calm. I think that's the most important thing I did today. Even though there were many ups and downs, I tried to stay tough."

Nishikori had lost seven of eight previous matches against Murray and said he battled early on. He believes the rain delay helped improve his focus.

"In the end I think I did really well, but first and before the rain delay I think I was little bit out of my concentration. I felt like I didn't know what to do," Nishikori said.

"But after the rain delay I think I was more focused and start playing better tennis, so I was getting more confidence during the match. And especially in the end. I think I wasn't making many unforced errors and playing great tennis. So confidence helped my game today."