Sixth seed Maria Sakkari came from behind to earn a dramatic win over qualifier Vitalia Diatchenko as the St Petersburg Ladies Trophy got under way on Monday.
The Greek beat her opponent in straight sets when they met in Adelaide last month, but the world number 89 put up more of a fight this time.
Sakkari, who reached the Australian Open fourth round, ultimately prevailed 3-6 6-4 7-6 (7-3) in two hours and 38 minutes after surviving an almighty scare.
Diatchenko twice failed to serve out the match in the deciding set and squandered a match point at 5-2, later paying the price in a tie-break where she fell 4-0 down and could not recover.
There was less drama for eighth seed Elena Rybakina as she earned a 6-3 6-4 win over Katerina Siniakova.
Anastasia Potapova came out on top in an all-Russian encounter with Liudmila Samsonova in the only other match to take place on day one of the WTA Premier event.
Belinda Bencic, Kiki Bertens, Petra Kvitova and Johanna Konta, the top four seeds, all got a bye in round one.
At the Thailand Open, fourth seed Zheng Saisai needed four set points before claiming a tense opener that set up a 7-6 (8-6) 6-0 triumph over Natalija Kostic.
Nao Hibino defeated Arina Rodionova 7-6 (7-5) 7-5, while there were also victories for Storm Sanders, Leonie Kung, You Xiaodi and home hope Peangtarn Plipuech.
Petra Martic will start her campaign against Wang Xiyu on Tuesday, with top seed Elina Svitolina not scheduled to play Bibiane Schoofs in her first-round contest until Wednesday.