Zhuhai, China: Defending champion Julia Goerges beat Elise Mertens on Thursday to book her place in the semi-finals of WTA Elite Trophy.
The fifth seed bounced back from a bruising defeat to Anett Kontaveit on Wednesday and overcame Mertens 6-2, 7-6 in a tense round-robin tie in Zhuhai, southern China.
Goerges, 29, was pushed all the way in the second set by her 22-year-old Belgian opponent, but the German clinched the nailbiting tiebreak 7-5 at the Hengqin International Tennis Center.
The straight sets victory was enough to take her to the top of the group, and the world number 14 jumped with joy and punched the air in celebration.
Earlier, Australia's Ashleigh Barty beat an out-of-sorts French number one Caroline Garcia to keep her semi-final hopes alive.
Ninth seed Barty broke Garcia once in each set to win the round-robin tie 6-3, 6-4 in one hour and 16 minutes.
Barty, who lost to Aryna Sabalenka on Tuesday, now has to wait for the outcome of Garcia and Sabalenka's match to see if she will progress to the semi-finals on Saturday.