Iga Swiatek began her bid to regain the world number one ranking with a comeback win over Barbora Krejcikova in the WTA Finals group stages.
Poland's Swiatek trailed the Wimbledon champion by a set and double break before regrouping to win 4-6 7-5 6-2.
This was the 23-year-old's first match since her quarter-final US Open exit in September and first under new coach Wim Fissette.
"At the beginning I felt a bit rusty but I'm happy that I found a way to play a bit more solid," said Swiatek.
She and Aryna Sabalenka are in contention to finish the year as the top-ranked player.