Despite beating beat Daria Kasatkina, Iga Swiatek was knocked out of the WTA Finals in Riyadh on Thursday.
Barbora Krejcikova defeated Coco Gauff to book her spot in the semi-finals of the WTA Finals and knock out defending champion Swiatek.
The Pole needed less than an hour to dispatch alternate Daria Kasatkina, who had replaced the injured Jessica Pegula, 6-1 6-0 in the opening match of the day.
But her chances of progress depended on the second match, and her luck was out as Wimbledon champion Krejcikova battled to a 7-5 6-4 victory over Gauff, whose place in the last four was already secured.
All three women finished the group stage with two wins from three matches but Krejcikova, the lowest-ranked player at the tournament, topped the pool by virtue of the best sets percentage, with Swiatek the one to miss out.
That came as something of a surprise to the French Open champion, with Swiatek stunned in her post-match press conference when reporters told her the win against Kasatkina had no bearing on her progress to the semi-finals.
"You mean it didn't matter," she asked the reporters, as she went on to insist she would be desperately disappointed to miss out on a place in the semi-finals.
That scenario transpired, with Swiatek insisting she was happy with her form at the WTA Finals despite a defeat against Gauff that ultimately ended her hopes of making the finals weekend.
"It was a pretty solid performance from me. I'm happy that I did everything to win it and glad I have two wins in the group now," said the Pole.
"I feel like I was spinning the ball well and picking the right shots to play faster and being solid.
"Thank you guys for the support. It means a lot and any place I go I hear this support.
"I haven't played in a while and I miss this feeling of the support."
Czech Krejcikova will take on Olympic champion Zheng Qinwen in the last four on Friday while Gauff meets world number one Aryna Sabalenka.
Krejcikova's shock Wimbledon win was the outstanding high point of what has been largely a disappointing season for her.
But she has risen to the occasion in Saudi Arabia, bouncing back from a three-set defeat by Swiatek in her opening match by beating Pegula and Gauff, saving 11 of 12 break points on Thursday.
"Definitely this is a big win for me," said the 28-year-old in her on-court interview.
"I'm really happy with the way that I played. Being able to qualify for the Finals and also reach the semi-finals, it's something unimaginable before this tournament. I'm very proud of myself and I'm looking forward to the new challenges."
