Top seed Daria Kasatkina has been knocked out of the WTA Elite Trophy, beaten 6-2 6-4 by Madison Keys.
Keys, 23, broke six times in a dominant display, leaving the Russian with one win and one defeat from her round-robin matches - and no chance of progressing.
The American just needs to win a set on Friday against China's Wang Qiang - who requires a straight-set victory to go through in Zhuhai.
All four group winners at the 12-player event will reach the semi-finals.
The invitation-only event features the top 11 players who did not qualify for last week's top-tier WTA Finals, with space for one wildcard.
Elsewhere, Anett Kontaveit beat defending champion Julia Gorges 6-2 4-6 6-4.
The Estonian, 22, broke the world number 14 three times to take the opening set.
Gorges, 29, fell heavily on the hard court during the sixth game of the second set, and needed ice to her right leg during the changeover.
The German fought back to win that set, but Kontaveit, 20th in the world, took the decider.
Kontaveit, seeded 10th, has now played both of her group matches, having lost her opener on Tuesday to Belgium's Elise Mertens, who still has to play Gorges.
Garbine Muguruza overcame a scare in the opening match of her group, beating Zhang Shuai 3-6 6-3 6-2.
China's Zhang, the wildcard entry in her home country, raced into a 3-0 lead in the opening set before Muguruza then left the court for a medical break. Zhang, the world number 36, then served out for the set.
The second set saw an improvement from the 25-year-old Spaniard, who had seven break points across two lengthy Zhang service games, before finally winning one to go 4-2 up. Muguruza, the only former Grand Slam champion at the event, served out to send the match to a final set.
The first five games of the decider went against serve before the former world number one won four in a row to kick off her tournament with a victory.