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.
Defending champion Swiatek will need to win the title to replace Sabalenka, while the Belarusian needs to win all three round-robin matches, external or reach the final.
Sabalenka began her campaign with victory over Zheng Qinwen on Saturday.
Coco Gauff beat fellow American and doubles partner Jessica Pegula 6-3 6-2 in the second Orange Group match on Sunday.
The top two players from each group advance to the semi-finals, with Sabalenka, Zheng, Elena Rybakina and Jasmine Paolini in the Purple Group.
The tournament is being held in Saudi Arabia for the first time – a move which has been criticised by some because of the country’s human rights record.
However, four unforced errors in a row from Pegula handed Gauff the break back, and the younger American promptly won four games in a row to clinch victory.
“Sometimes it was sloppy, sometimes it was great – but that’s tennis,” said Gauff.
