Defending champion Elina Svitolina stormed into the semi-finals of the season-ending WTA Finals after a commanding win over Simona Halep on Wednesday, while Canadian sensation Bianca Andreescu retired hurt against Karolina Pliskova.
Andreescu injured her left knee in the third game after attempting to return a wide serve and received heavy strapping during the subsequent medical timeout.
The 19-year-old gamely fought on but was noticeably hobbled and retired after the first set, which Pliskova won 6-3 in 51 minutes.
"I was really pumped for today but I feel sorry that she had to retire," Pliskova said after the match.
Svitolina will finish top of Purple Group after taking advantage of an error-strewn Halep to win 7-5, 6-3 in one hour and 39 minutes at the Shenzhen Bay Sports Centre.
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Svitolina is the first player through to the semi-finals, having also beaten world number two Pliskova in straight sets on Monday. Wimbledon champion Halep will play Pliskova on Friday to decide the group´s second spot.
Svitolina had the better of long baseline rallies against an uncharacteristically errant Halep, who finished with 38 unforced errors.
"It´s about managing attack and defense for me," Svitolina said. "I´ve been working on this. That´s working well this week."
After a slow start, Halep came back into the contest and a powerful forehand winner down the line clinched her break in the fifth game before the players held serve.
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A sloppy Halep misfired in the 12th game as she handed Svitolina the first set with a slew of unforced errors.
Halep started well in the second set with an early break before falling away against a more consistent Svitolina.
The result broke a deadlock between the pair with Svitolina now holding a 5-4 edge and exacting revenge for a semi-loss to Halep at Wimbledon in July.
The 25-year-old is hoping to end a barren season on a high having failed to win a title since last year´s WTA Finals triumph.
Halep said she had to sharpen her game to stay in the tournament. "I really want to win because I want to qualify from this group," she said.
"Hopefully I can recover because I´m a little bit tired and play better than today," she added.