Dutch top seed Kiki Bertens beat Croatia's Donna Vekic for the third consecutive time this year with a 7-6(5) 6-2 victory in their round robin match at the WTA Elite Trophy in Zhuhai on Tuesday.
Bertens, playing in her seventh tournament since her U.S. Open third round exit, was pushed to the limit in an absorbing opening set that lasted an hour and 20 minutes, with a number of games going to deuce and plenty of break points available.
There were 15 break points in the match, with Bertens converting four and Vekic winning two.
"The first set was really tight, so it was just a few points here and there," Bertens told reporters. "I was just trying to push myself all the time.
"It was tough... mentally but also physically. We were both struggling a little bit. But from 5-4 down I played two really good points."
While the first set went to a tiebreak, Bertens shifted gears in the second to take a 5-0 lead after Vekic dropped three consecutive service games. Despite dropping serve late in the second, Bertens wrapped up the match.
In the other group, fourth seed Aryna Sabalenka overcame Greek ninth seed Maria Sakkari with a straight sets victory, winning 6-3 6-4 in a match where both players won a high percentage of first service points.
Belarusian Sabalenka won 86% of her first service points despite making eight double faults and needed only one break of serve in each set to clinch the contest.
American third seed Madison Keys was no match for China's Zheng Saisai, falling to a 6-4 6-2 defeat.
Local favourite Zheng's superior court coverage proved to be a weapon whenever Keys attempted to lure her to the net, and the American was broken six times in the match.