Zhuhai - Slovakia's No 1 Magdalena Rybarikova beat top seed and French star Kristina Mladenovic at the WTA Elite Trophy on Wednesday in a tight match at the round robin tournament.
Rybarikova, who reached her maiden Grand Slam semi-final at Wimbledon this year, overcame Mladenovic 7-5, 1-6, 7-6 (7/5) in two hours and 48 minutes at the Hengqin International Tennis Centre in Zhuhai.
The Slovakian, ranked 22 in the world, started off well by firing two aces in the first set.
Mladenovic stormed back in the second, winning six out of seven games while Rybarikova had a medical time out.
In the third set both players put up a strong fight to take it to a tiebreaker, and Rybarikova squandered a total of six match points before she finally sealed her victory.
"(There were) ups and downs from my side, but... there's a lot of things to take out from this match, lots of positives," Mladenovic told journalists afterwards, adding that Rybarikova was a "great player".
Twenty-four-year-old Mladenovic is the number one seed at the season-ending tournament and ranked at a career-high number 10.
The round robin format means she still has a chance to qualify for the semis.
But her first-match loss in Zhuhai follows a recent poor run, including an upset by Croatian Jana Fett at the Japan Women's Open in September, where she was also top seed.
Earlier in the season she reached the semi-finals at Indian Wells - a result which saw her break into the world top 20 for the first time, temporarily overtaking Caroline Garcia as French number one.
"(It was) a pretty unique season," she said when asked about her performance.
"The second part is dramatic, is terrible. The first part is also dramatic but in a positive way."
However, despite "the tricky journey", the French No 2 said she had improved a lot.
Later, the youngest player in the tournament and ninth seed Australia's Ashleigh Barty cruised to victory over Russian Anastasia Pavlyuchenkova in just one hour and 11 minutes, with scores of 6-4, 6-1, firing nine aces.