Japan’s Kei Nishikori says his US Open win over world No.1 Novak Djokovic has been a turning point in his career and given him confidence that he can beat the very best.

Nishikori upset Djokovic in four sets in the US Open semi-final, before falling to Marin Cilic in the final.

He said the win over the top Serb to become the first man from an Asian country to reach a grand slam decider had changed his mindset.

“It was one of the best matches I had last year against one of the best players on the tour,” Nishikori said.

“That US Open changed me a lot.

“I won two titles after that and I had a lot of confidence to beat him and also (Stan) Wawrinka, (Milos) Raonic – I had some great matches in the US Open so it was a great moment for me.”

The 25-year-old is defending his title at the eight-man invitational Kooyong Classic in Melbourne as he warms up for the Australian Open.

While rain prevented any play on day one, Nishikori hoped the round-robin event would again be a springboard for success, with his ranking surging last year from world No.17 to a career-high five.

At Melbourne Park he lost to Rafael Nadal in the round of 16 but was still pleased with his start.

‘I’ve got great memories from this tournament and I played really good matches to win against Tomas (Berdych) in the final.

“I then lost to Rafa (Rafael Nadal) at the Australian Open but that was a great match so I was really happy with what I did last year.”

Nishikori said he had prepared well for 2015, spending two weeks training with his coach Michael Chang.

The former French Open champion will be court-side in Melbourne to watch his charge.

Nishikori said that 12 months into their partnership, he felt much more comfortable.

“He’s been giving me some good tips to get better to go to the next level.

“He’s a great coach – he’s tough but he’s given me great practice and I’ve had a great off-season.

“I think I’m ready for the Australian Open.”