Osaka stunned Serena Williams in straight sets to claim her and Japan's first ever Grand Slam title in New York last month and she backed that up with a run to the final at the Pan Pacific Open to all but ensure she would make her debut in Singapore.

After claiming victory in her opening match at the ongoing China Open in Beijing on Monday, Osaka joined Romanian world number one Simona Halep and German Wimbledon champion Angelique Kerber as qualifiers for the WTA Finals.

"Qualifying for the WTA Finals is a huge accomplishment," said Osaka, who beat Frenchwoman Caroline Garcia to win a junior version of the Singapore tournament three years and will be returning for the first time as a senior.

"Winning the WTA Rising Stars Invitational in 2015 helped give me the confidence to play on the big stages, so I am excited to go back to Singapore and compete with the top players of the season."

Big-hitting Czech Petra Kvitova and Australian Open champion Caroline Wozniacki of Denmark, who won last year's WTA Finals, are also poised to qualify for Singapore but the remaining spots appear to be a four-way battle for three places.

American Sloane Stephens, Ukrainian Elina Svitolina, Czech Karolina Pliskova and Kiki Bertens from the Netherlands will fight it out to complete the field for the Oct. 21-28 tournament being held for the fifth and final time in Singapore.