After being upset in her opening match against eighth-seeded Beatriz Haddad Maia on Tuesday, the American player had to win against No.20-ranked Garcia to keep her semifinal hopes alive.
But despite Keys firing six aces, the ninth-seeded Frenchwoman forced the only break of serve in the match to clinch the first set. Garcia then held her nerve through a tighter second set to seal her first win over the 11th-ranked Keys since a Fed Cup playoff in 2014.
Garcia plays Haddad Maia on Friday in a straight shootout to win the Camellia group and advance to the semifinals.
In a see-saw match where neither player could assert themselves for long periods, Kasatkina wrestled back momentum in the decider and reeled off six of the final seven games to clinch the match in two hours and 10 minutes.
The sixth-seeded Russian next plays Magda Linette, who lost to Krejcikova in her opening match, on Friday knowing a win will take her through to the semi-finals. If Linette wins, the semifinal spot will be decided by sets or games won between the three players.
The 12-player tournament is the first postseason event on the women’s tour. It features the 11 highest-ranked singles players who did not qualify for the WTA Finals in Cancun, Mexico, which will be held next month. Zhu Lin, ranked 37th, is the final entry as a wild-card.
Players are divided into four groups of three players with the winner of each group advancing to the semi-finals on Saturday. The final is scheduled for Sunday.