Melbourne: The fatigue in Kei Nishikori's legs was obvious as he dragged himself up several flights of stairs to a television interview after his four-set victory over France's Julien Benneteau at the Australian Open yesterday.

The 22-year-old had just battled for three hours, 25 minutes to win 4-6 7-6 7-6 6-3 and propel himself into the last 16 of the grand-slam event, becoming the first Japanese to achieve the feat since tennis was declared open in 1968.

"I am very excited to get to the round of 16," the slightly-built Nishikori said on a rooftop overlooking the Melbourne Park courts.

"That's my best result in a grand slam and I will try to win the next one."

Nishikori is one of the most recognisable faces in his home country having become the first Japanese man to take an ATP tour title in 16 years when he won at Delray Beach in 2008.

The 22-year-old has his own computer game and a truckload of commercial sponsors ranging from noodles to clothing. He is acutely aware of his fame in his home country, if reluctant to discuss it.

"It's not really for me to say," the smiling Nishikori said when asked how famous he was in Japan. "But I'm quite popular I guess. It's hard to walk in Tokyo especially."

His only goals for 2012 were to keep his ranking and hopefully crack the top 15 by the end of the year, he said.