WTA Finals holder Caroline Wozniacki and former champion Petra Kvitova have clinched places in this month's season-ending tournament in Singapore, the WTA announced on Thursday.
The pair join world number one Simona Halep, Angelique Kerber and Naomi Osaka who have already qualified for the Oct. 21-28 tournament at the Singapore Sports Hub.
"Winning the WTA Finals last year was a huge accomplishment for me and helped my confidence leading into this season," Wozniacki, who won the Australian Open in January, said.
"I look forward to coming back to Singapore to try and defend my title," the 28-year-old Dane added.
Wozniacki secured her the spot after a routine 7-5, 6-4 win against Estonia's Anett Kontaveit at the China Open in Beijing on Thursday.
Czech Kvitova, who won the WTA Finals title in 2011, has qualified for the first time since suffering career-threatening injuries to her left playing hand after a 2016 stabbing that kept her out for six months.
Kvitova, who lifted the Wimbledon trophy in 2011 and 2014, required surgery after trying to protect herself from a man wielding a knife who gained access to her apartment.
"It will be my first time back there (the WTA Finals) since I came back to tennis so it means a lot to me and has always been one of my big goals for the season," Kvitova, who has won five titles this season, said.
The top eight singles players at the $7 million prize money event will compete in a round-robin format with the winner taking home the Billie Jean King Trophy.
The top eight doubles teams will compete for the Martina Navratilova Trophy.
Zhang downs Kerber to set up Osaka clash in Beijing
Zhang Shuai stunned Wimbledon Champion Angelique Kerber 6-1, 2-6, 6-0 in the China Open on Thursday to set up a quarter-final clash with Naomi Osaka.
China's Zhang broke Kerber's serve five times and fired 22 winners to seal the victory in an hour and 27 minutes in her second meeting with the German.
"I can defeat a former number one, a Grand Slam champion, this is something I'm proud of for the rest of my life," an elated Zhang said.
The 29-year-old looked in complete control against Kerber, cruising through the first set before the German levelled the contest.
Yet Kerber struggled to keep her unforced errors count down, making 36 in the match, and her challenge ended in a final set rout.
Up next for Zhang is U.S. Open champion Osaka, who thumped Julia Goerges 6-1, 6-2 and described the performance as her best of the tournament so far.
"I know I played well today, better than all the other days," Osaka said. "Key today was staying focused and trying to return well because we both have really good serves."
Zhang has a 2-2 win-loss record against Osaka and beat the Japanese player in their last meeting in Madrid this season.
China's Wang Qiang advanced with a 6-4, 6-4 win over world number seven Karolina Pliskova in an hour and 37 minutes while Kiki Bertens of the Netherlands crashed out after a 6-4, 6-3 defeat by Katerina Siniakova.
Australian Open champion Caroline Wozniacki clinched a place in the season-ending tournament alongside Petra Kvitova after beating Estonia's Anett Kontaveit 7-5, 6-4.
The in-form Aryna Sabalenka knocked out defending champion Caroline Garcia 5-7, 7-6(3), 6-0.