Defending champion Elina Svitolina stormed into the penultimate stage of the season-ending WTA Finals after a commanding straight-sets victory over Simona Halep on Wednesday.
The world No 8 took advantage of an error-strewn Halep and prevailed 7-5, 6-3 in one hour and 39 minutes at the Shenzhen Bay Sports Centre.
Svitolina is the first player through to the semi-finals, having also beaten world No 2 Karolina Pliskova in straight sets on Monday. Halep still has a chance of qualifying having overcome US Open champion Bianca Andreescu in a three-set thriller in her opener.
The 19-year-old US Open champion, meanwhile, was forced to retire from her match against Pliskova after injuring her left knee midway through the third game.
No 2 seed Pliskova had won the opening set 6-3 before Andreescu, with her knee heavilly strapped, decided she could not continue.
"I stepped weirdly on a return," said Andreescu, who will have a scan on her injured left knee before deciding whether she will play on in Shenzhen.
"I heard my knee crack. It kind of went inwards. Putting pressure afterwards on it really bothered me. I could barely bend my knee.
"But I fought with the pain as much as I could. At some point an athlete has to say 'stop' and just listen to their body. That's what I did."
Andreescu took an injury time out that lasted more than eight minutes before returning to action, but with her movement severely curtailed.
"I was actually looking forward to this match because I think I started well with a good match against Svitolina," said Pliskova, who lost her opener against the Ukrainian in straight sets. "I was really pumped for today but I'm sorry she had to retire.
"Everybody is a little bit tired at this part of the season so it's tough to play, but hopefully she can be ready for her next match, and if not then Australia."
Pliskova will now face Halep in the pair's final game in the Purple Group on Friday knowing a win will take her into the semi-finals alongside Svitolina.
In the earlier match, Svitolina had the better of long baseline rallies against an uncharacteristically errant Halep, who finished with 38 unforced errors.
"It was an extremely physical match and we were both chasing a lot of balls and we left a lot of energy out on the court," said Svitolina.
"I was still playing very solid today and my defence was very good so I'm very happy about that.
"I was expecting a tough match here when I arrived and I had to stay really focused on each game of each match and hopefully I can keep up this level and play strong in the next match as well."
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.
Like how she started, 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 not captured a title since last year's WTA Finals triumph.