Former world number one Garbine Muguruza was beaten 7-5, 6-4 by Aryna Sabalenka in the China Open second round on Tuesday while an ailing Jelena Ostapenko lost 6-0, 6-0 to Wang Qiang.
Sabalenka, who claimed her second title of the season at the Wuhan Open last week, edged a tight opening set and the Belarusian took control in the next to overpower Spaniard Muguruza and secure victory in an hour and 46 minutes. Former French Open champion Ostapenko struggled with a wrist injury before losing to local hope Wang in 55 minutes.
Guangzhou champion Wang, who has won 14 of her last 17 matches, next plays former world number one Karolina Pliskova or Aliaksandra Sasnovich. World number three Angelique Kerber fought back from 5-3 down in the first set to beat Carla Suarez Navarro 7-6(4), 6-1.
US Open champion Naomi Osaka crushed Danielle Collins 6-1, 6-0 to set up a clash with 10th seed Julia Goerges who beat the Japanese the last time they met in Charleston this season. American Sloane Stephens took advantage of an error-prone display by China's Zheng Saisai to win 6-1 6-3 and set up a clash with Dominika Cibulkova who beat Daria Gavrilova 6-3, 6-3.
Osaka secures WTA Finals berth
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 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.
Del Potro powers past Ramos-Vinolas in Beijing opener
US Open finalist Juan Martin del Potro swatted aside Spain's Albert Ramos-Vinolas 7-5, 6-2 on Tuesday to reach the China Open second round.
Del Potro, playing his first match since losing to Novak Djokovic in the US Open final last month, looked in fine form as he fired 10 aces and won 86 percent of points on his first serve to seal victory in 90 minutes.
The 30-year-old Argentine can qualify for next month's ATP Finals in London for the first time since 2013 if he reaches the final in Beijing. He plays Russia's Karen Khachanov next.
Rafael Nadal, Djokovic and Roger Federer have secured their places in the season-ending tournament.
Bulgaria's Grigor Dimitrov, a finalist in Beijing two years ago, began his campaign with a solid 7-5, 6-3 victory over American Tennys Sandgren.
"It's never easy when you've never played against a guy," said world number eight Dimitrov, who next faces Serbia's Dusan Lajovic.
"So it took me quite a few games to kind of get in a rhythm, see what kind of game plan he had (and) just try to get comfortable in the match."
Spain's Fernando Verdasco was made to work hard before beating France's Gael Monfils 2-6, 7-6(3), 7-6(5) in two hours and 23 minutes.
Top seed Cilic out of Japan Open
Top seed Marin Cilic crashed out of the Japan Open in a shock 3-6, 6-4, 7-6 (7/1) defeat to Germany's Jan-Lennard Struff in the first round on Tuesday.
Struff smashed the breaker, snaffling it 7-1 with his ninth ace to complete the upset after two hours, 18 minutes.
He next plays Frenchman Jeremy Chardy, who edged a war of attrition with Bosnian Damir Dzumhur 4-6, 6-3, 6-3.
Earlier, three-time Grand Slam winner Stan Wawrinka beat Taylor Fritz 6-3, 6-4 while eighth seed Richard Gasquet also advanced, the Frenchman ousting another American, Denis Kudla, 7-6, 6-3.
Frances Tiafoe restored some pride for the United States by beating Germany's Maximilian Marterer 7-5, 6-4.
Federer focusing on future with new sponsor Uniqlo
Roger Federer said on Tuesday his decision to end a 20-year association with Nike and embark on a new chapter with Uniqlo was influenced by the Japanese clothing company's commitment to stay with him long after his playing days are over.
While no financial details have been announced, media reports have said the new deal would be worth around $30 million a year, compared with the $10 million a year agreement Federer had with Nike.
The 37-year-old, who has won a record 20 Grand Slam singles titles, signalled the end of his association with Nike in July when he walked out onto Wimbledon’s Centre Court dressed in Uniqlo apparel.
Federer said the belief shown in him by Uniqlo's CEO Tadashi Yanai and Executive Creative Director John Jay had been key.
"John Jay in New York, where I had an event there, said it very nicely: 'One day I will retire from tennis but I will not retire from life,'" said Federer, who was presented as Uniqlo's new global brand ambassador.
"Life will go on and Uniqlo and Mr. Yanai believed in me very strongly as being very important to their brand, even though maybe my playing days are going to come to an end at some point."
By incorporating Federer in their LifeWear range, Uniqlo appear to see the Swiss as a brand off court as much as on it.
Halep suffers herniated disc
World number one Simona Halep's participation in this month's WTA Finals was thrown into doubt after a scan on Tuesday revealed she had suffered a herniated disc in her back.
French Open champion Halep was injured while training at last week's Wuhan Open, where she lost in the second round to Slovakia's Dominika Cibulkova.
Romanian Halep aggravated the problem during her China Open first-round match on Sunday against Ons Jabeur and was forced to retire after losing the first set.
"I had an MRI on my back and found out I have a disc hernia," Halep said on Twitter.
"I will discuss with doctors in the next few days but hope to be back soon and will keep you updated."
Halep, who won her maiden Grand Slam trophy in Paris this year, became the first player to qualify for the season-ending WTA Finals in Singapore from Oct. 21-28.