Tokyo--Record-breaking Japan superstar Kei Nishikori rose to fourth in Monday's new world rankings, equalling Kimiko Date-Krumm as his country's highest-ranked tennis player.

The 24-year-old, who is the top-ranked Asian-born man ever, tweeted: "Just saw the new rankings. Very proud of another step...#4 this week."

Nishikori, last year's US Open runner-up, now trails only Novak Djokovic, Roger Federer and Rafa Nadal after leapfrogging Britain's Andy Murray, meaning he will avoid the top three until the semi-finals at the major tournaments.

"He has the touch of a genius," former Japan number one Shuzo Matsuoka told AFP. "He has the imagination and shots you just can't teach."

Nishikori recently won his third successive Memphis Open, his eighth ATP Tour title. He is fast closing in on Nadal and trails the 14-times grand slam champion by just 260 ranking points.

"It's an achievement that's almost impossible to explain," Matsuoka told Japan's Sankei Sports, comparing the skinny Nishikori to a sumo grand champion. "He's really playing 'yokozuna'-grade tennis."

Nishikori burst onto the scene as an 18-year-old by winning in Delray Beach as a 244th-ranked qualifier in 2008, and is a huge celebrity in Japan.

Millions woke up at the crack of dawn to watch his bid to become the first Asian man to win a grand slam at last year's US Open, where he lost in the final to Croatian Marin Cilic.

China's Li Na blazed a trail for Asian tennis players by reaching number two in the women's WTA rankings last year after winning the Australian Open, capping a remarkable career in which she also captured the 2011 French Open.

She retired seven months later with knee trouble.

Nishikori's coach Michael Chang, whose parents came from Taiwan and who was raised in the United States, is a former world number two who won the French Open in 1989.