Stan Wawrinka insists he is playing better than he was when he won the Australian Open a year ago, but feels his opponents have also improved.

The defending champion progressed to the semi-finals at Melbourne Park with a 6-3 6-4 7-6 (8-6) victory over Kei Nishikori on Wednesday.

Such a comprehensive win was unexpected, with Wawrinka hitting 46 winners in a good display on Rod Laver Arena.

Asked if he was reaching similar levels to 2014, the Swiss star said he was surpassing them.

"No, I think I play better," Wawrinka said.

"But I think we all improve every year. I'm more aggressive. I'm more confident with my game when I come to the net.

"Again, it's a grand slam. You play every two days.

"Today was a great level, was a great match. Now I'm going to enjoy a little bit, watch who's going to win tonight and get ready for the semi-final."

Wawrinka was delighted with his performance against Nishikori, particularly his serving.

He sent down 20 aces and gave up just four break-point opportunities.

"For sure today I was serving really well. I'm happy with that part of my game," Wawrinka said.

"It's never easy to break Kei because he's playing so well. You need to be focused on what you need to do. You need to change the speed. You need to change where you serve also.

"I think it was one of my best match if I look at that."