Garbine Muguruza reached the semi-finals of the WTA Elite Trophy after saving three match points in her showdown with Anastasija Sevastova, while Ashleigh Barty and Madison Keys also qualified for the last four.
Muguruza was on the brink of elimination in Zhuhai on Friday, but the two-time grand slam champion fought back to win 6-7 (4-7) 6-2 7-6 (7-1).
Sevastova was twice a break up in the final set, yet the battling seventh seed rallied in a decisive match to prolong her season.
Second seed Sevastova had treatment on her back after losing the second set and did not appear to be troubled as she moved into a 2-0 lead, then broke again to go 5-4 up.
Muguruza refused to be beaten, though - the Spaniard preventing Sevastova from serving out the match and bossing the tie-break to win the Camellia Group.
Barty advanced for the second consecutive year courtesy of a straight-sets triumph for Caroline Garcia over Aryna Sabalenka, which was not enough to see Garcia through.
Garcia could only progress by losing fewer than seven games, so a 6-4 6-4 Orchid Group victory was in vain.
Wang Qiang defeated Keys 1-6 6-3 6-1 in the final round-robin match, but it is the American who qualifies from the Azalea Group to join Muguruza, Barty and Julia Goerges in the last four.