The Japanese star believes pressure may have played a part in his 6-3, 6-4, 7-6 (8-6) defeat by the Swiss defending champion, but says overall he is still pleased with his progress.
Nishikori said: "I may have felt a little bit of pressure. But he was serving really well today because I usually return well and break in a couple games.
"His serve was clearly superior. I wasn't able to read it. He also had me under pressure with his strokes from the start and I started pressing.
"So it was tough to find my game today and he was playing really aggressive, great forehand, backhand."
He added: "It wasn't really a bad week. It's not easy come quarter-final time at the Grand Slams. I have to keep doing this. I could be better. But I need more of these experiences, playing tough all the time, playing a lot of matches. Especially in Grand Slam, there is more pressure.
"I don't know, you get more experience on Grand Slams I think. Hopefully I can keep playing good. Yeah, it's great start in Brisbane and here. Hopefully I can keep going like this."