Kiki Bertens of Netherlands hits a return against Ashleigh Barty of Australia during their women's singles match in the WTA Finals tennis tournament in Shenzhen. - AFP
Shenzhen - Bencic advances from Red group after the Swiss beat Petra Kvitova 6-3 1-6 6-4, which leaves the Czech winless in her opening two matches.
Ashleigh Barty surrendered a one-set lead to crash to a 3-6, 6-3, 6-4 loss at the hands of late replacement Kiki Bertens at the WTA Finals on Tuesday as the world number one's prospects of advancing to the semi-finals suffered a blow.
Barty was facing the Dutchwoman after she took Naomi Osaka's place in the draw following the Australian Open champion's withdrawal with a shoulder injury and Bertens made the most of the opportunity.
After feeling her way through the first set, the world number 10 - who reached the semifinals of last year's tournament - raised her game to hand Barty her first loss of the competition.
"In the beginning I think was not playing so well," said Bertens.
"I had to feel the court a little bit more, but I think I was getting better and better in the rhythm, trying to play aggressive and trying to come to the net.
"I think I did pretty well."
Barty's status as world number one in the year-end rankings was confirmed following her win over Belinda Bencic on Sunday and the Australian looked impressive in the opening set, even as both players had trouble holding their serve.
Bertens, though, turned the tables in the second set, breaking the 23-year-old in the penultimate game to level the scores and take the match into a decider.
She carried that form into the final set and, as Barty struggled on her own serve, Bertens closed out the match to record her first-ever win over the French Open champion in five attempts.
"We know we're still alive in the tournament," said Barty. "That's the beauty of round-robin. It's a different format.
"But it's not going to stress me out too much. We'll hit the practice court tomorrow and come back on Thursday, try to play for a spot in the semis."
Barty and Bertens were joined on one win apiece at the end of the second round of matches in the Red Group by Bencic after the Swiss beat Petra Kvitova 6-3 1-6 6-4, which leaves the Czech winless in her opening two matches.
After a solid start by both players, Kvitova found the net with a volley from close range to drop her serve in the seventh game and, two games later, surrendered the opener when she hit a double fault on set point.
Kvitova was relentless in the second set as consistent serving and the strength of her returns left Bencic increasingly frustrated, with the Swiss slamming her racket into the ground on the way to a comprehensive loss.
But the 22-year-old showed her resilience as she steadied herself in the final set, claiming the vital break in the penultimate game before closing out the win.