US Open champion Naomi Osaka has become the third player to secure a berth at the season-ending WTA Finals later this month after the 20-year-old from Japan amassed enough points in the Race to Singapore to qualify for the eight-woman event.

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 of the Pan Pacific Open to all but ensure she would make her debut in Singapore.

After beating Kazakhstan's Zarina Diyas 6-4, 6-3 in her opening match at the China Open in Beijing on Monday, Osaka joined Romanian world No 1 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 ago.

"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."