Top seed Kiki Bertens enjoyed a hard-fought win over eighth seed Donna Vekic in the Azalea Group at the Hengqin Life WTA Elite Trophy in Zhuhai.
Bertens edged a tie-break to decide an opening set which lasted for 80 minutes and raced into a 5-0 lead in the second before taking it 6-2 to complete victory in a minute shy of two hours.
"The first set was really tight, so it was just a few points here and there," Bertens said. "I just was trying to push myself all the time.
"It was tough I would say, mentally but also physically. We were both struggling, I think, a little bit. But from 5-4 down (in the tie-break) I played two really good points."
China's Zheng Saisai thrilled the home crowd with victory over third seed Madison Keys, winning 6-4 6-2 in the Orchid Group.
"I am pretty happy about the win today because I didn't expect to win today," admitted Zheng, who received a wild card into the 12-woman event. "I was just going to fight for it.
"I think I played pretty solid today. She didn't put many first serves in, which gave me more opportunities to go into the rallies and start to run her (around). So I think that's the key for today."
In the day's other game in the Rose Group, fourth seed Aryna Sabalenka beat ninth seed Maria Sakkari 6-3 6-4.