After confidently dealing with the threat of ninth seed David Ferrer in straight sets, Kei Nishikori said he is playing close to "100 per cent" at Melbourne Park.

World number five Nishikori was a class above Ferrer on Rod Laver Arena, dropping serve only once as he triumphed 6-3 6-3 6-3.

The Japanese star was the aggressor throughout with 43 winners to Ferrer's 14.

And, with defending champion Stan Wawrinka waiting in the last eight, Nishikori feels he is playing some of his best tennis in Melbourne.

"I was feeling a lot of confidence. Against him I had nothing to lose," Nishikori said.

"So I played almost 100 per cent tennis, [with a] lot of confidence.

"I was playing really aggressive, good forehand, and serving really well.

"Obviously it's going to be a tough opponent next match, but I've been playing well, so it's going to be exciting match."

Nishikori has only dropped two sets at the Australian Open in 2015, but he will face a stern test against Wawrinka, who has eased his way into the quarter-finals.

But Nishikori will take heart from his five-set win over the Swiss at the US Open last year.

"For sure that gives me confidence. I beat him in the US Open," Nishikori added.

"It's not like I can't beat him. It's going to be a fun match for sure."