Debutant Dayana Yastremska knocked Donna Vekic out of the WTA Elite Trophy and Maria Sakkari was eliminated by Elise Mertens on Wednesday.
Yastremska, the youngest player in the tournament at the age of 19, won her Azalea Group opener 7-6 (8-6) 6-2 in Zhuhai.
The Ukrainian teenager unleashed a barrage of ferocious forehand winners in a high-quality contest, which proved to be Vekic's last of the season.
Rising star Yastremska rallied from 5-3 down in the tie-break after the pair could only force three break points between them in a serve-dominated first set.
Vekic did her best to withstand the force of the 10th seed in the second, but a fierce forehand winner put Yastremska a break up and a potent backhand return made it 5-2.
Yastremska served out the match and will face top seed Kiki Bertens for a place in the semi-finals.
Mertens earlier sent Sakkari out with a 6-2 3-6 6-1 victory in the Rose Group.
Sixth seed Mertens will face her doubles partner Aryna Sabalenka with a place in the last four on the line after beating Sakkari for the first time in five years.
Mertens won four games in a row in the final set to send Sakkari packing.
Sofia Kenin won the final match of the day, starting the tournament with a 6-4 6-4 success over fellow American Alison Riske.