Defending champion Coco Gauff fought back to beat Belinda Bencic 4-6, 7-6(4), 6-2 in a tense encounter Tuesday and reach the China Open quarter-finals.
Gauff next plays either Eva Lys of Germany or fellow American McCartney Kessler in Beijing.
"It was a tough match," Gauff said. "I had chances in the first to close it out but overall I'm happy with how I fought. She was being really aggressive."
There were frustrations on both sides of the court at a largely empty stadium as the players switched between one half darkened by shade and the other in the blazing sun.
There was a flashpoint between the two players during a changeover in the second set when Switzerland's 15th seed Bencic said, "Your team is chatting. I'm too old for these mind games, okay?"
"You're the one playing the mind games," Gauff, the second seed, shot back.
The 21-year-old Gauff kept it together to win the tiebreak when Tokyo Olympic champion Bencic double-faulted on set point and threw her racquet in anger.
The world number three Gauff broke early in the third set and carried that momentum through to win when a flagging Bencic returned into the net.
With her last-16 victory, Gauff qualified for the WTA Finals in Saudi Arabia in November.
"Happy to qualify once again. Happy to be back in Riyadh and I'm glad I was able to do it here," Gauff told the on-court interviewer.
"It's been a tough tournament so far, but I'm happy to get through."