Caroline Wozniacki brings the curtain down on a career that saw her win 30 WTA titles, with her sole Grand Slam triumph coming in 2018 at Australian Open.
Serena Williams, at her imperious best, rapidly eliminated third-seed Amanda Anisimova 6-1, 6-1 to set up a showdown against Jessica Pegula.
Serena Williams defeated Laura Siegemund 6-4,6-3 to reach the semi-finals of the WTA Auckland Classic while Caroline Wozniacki beat defending champion Julia Georges 6-1, 6-4.
Caroline Wozniacki, who turned professional at the age of 15 in 2005, spent 71 weeks at the top of the WTA rankings after first becoming the world's best player in October 2010.
Japanese Naomi Osaka will play world number one Ashleigh Barty of Australia in Sunday's championship match in Beijing.
China Open: Naomi Osaka said that she felt she had been "counted out" after hitting poor form following her Australian Open triumph in January.
It completed another bad day for organisers who lost their main attraction on the eve of the tournament, Naomi Osaka.
Maria Sharapova won 6-4, 4-6, 6-3 with the roof closed on Rod Laver Arena.
The pressure on the reigning French Open champion will only increase in her next round.
The Russian five-time Grand Slam champion was forced to stay up late in her second-round match.
The 31-year-old has only conceded three games en route to round three at Melbourne Park, where she won the title in 2008.
Roger Federer is working towards a third successive Australian crown and a 21st major victory.
Serena Williams is gunning to match Margaret Court's record of singles majors and claim an eighth Australian Open crown.
Kvitova has now lost both her matches and needs results to go her way in the White Group to stay afloat in the season-finale.
The 28-year-old Caroline Wozniacki had won the China Open in 2010.
Caroline Wozniacki and Angelique Kerber suffered shock defeats at the hands of less fancied opponents.
World number two Caroline Wozniacki and Wimbledon champion Angelique Kerber eased through their opening matches at the Wuhan Open in China on Tuesday.
Romania's Simona Halep continued to lead Women's Tennis Association (WTA) rankings released on Monday, ahead of Denmark's Caroline Wozniacki.