Singapore - World number one Simona Halep crashed out of the WTA Finals on Friday as French debutante Caroline Garcia stunned Caroline Wozniacki to reach the last four.
Halep needed a win to keep her campaign alive but she was sent packing by the already eliminated Elina Svitolina, who won 6-3, 6-4 in 71 minutes.
It means Garcia, the lowest-ranked player in the draw, tops Red Group after she fought back from behind to upset Wozniacki 0-6, 6-3, 7-5 earlier on Friday.
Garcia will now play American veteran Venus Williams on Saturday, while Denmark's Wozniacki faces Karolina Pliskova in the other semi-final at the Singapore Indoor Stadium.
Even though her campaign ended in disappointment, Halep will still finish the year as world number one if Pliskova does not lift the trophy on Sunday.
"I just felt 100 percent that the court is not for me and I cannot finish a point," the Romanian said. "So it was a little bit tough to find my rhythm and also to make a winner."
Svitolina said she happy to leave Singapore with a win after losing her first two matches.
"I was sad with the way I played this week," she said. "I had nothing to lose in this match. It means a lot (to win)."
Svitolina went for her shots and dictated from the back of the court, rattling a shaky Halep, who had suffered a big loss to Wozniacki in her previous match.
The Ukrainian dictated from the start, breaking Halep's tentative serve straight away and winning the opening three games before claiming the first set in 31 minutes.
Halep fought back in the second set with an early break but she was broken straight back and her head dropped when Svitolina claimed what turned out to be the decisive break in game seven.
Earlier Garcia, the world number eight, was pinching herself after her thrilling victory over Wozniacki - her first win in three career meetings with the Dane.
Garcia, who won her last two tournaments to reach the Finals, was two points from elimination in the 10th game of the third set but she dug deep to hand Wozniacki her first defeat of the competition.
Even so, Garcia had to endure a nervy wait until Svitolina beat Halep to send her into the last four.
"It was kind of weird, actually, to be here. I mean, I qualified last minute, two weeks before. I wanted to keep improving like I did. That's why I think I won these two matches," Garcia said.
Wozniacki, who has been in sensational form in Singapore, described her first loss as "annoying".
"I feel like I should have won that match, but it is what it is," she said. "I had the chance to serve it out and I didn't. That's really it."
Wozniacki seemed headed for a third straight win after dominating in the early stages, making just one unforced error as she raced through the first set in 22 minutes.
But the match took an unexpected turn in the second set when Wozniacki had a time violation and argued with the umpire during the third game.
Garcia capitalised and won four straight games en route to levelling the match, before outlasting Wozniacki in a tense third set.
Results from the round-robin stage of the WTA Finals tennis in Singapore on Friday (x denotes seeding):
Caroline Garcia (FRA x8) bt Caroline Wozniacki (DEN x6) 0-6, 6-3, 7-5
Elina Svitolina (UKR x4) bt Simona Halep (ROM x1) 6-3, 6-4