French Open champion Simona Halep has pulled out of the Kremlin Cup with a back injury, casting further doubt on her participation in the WTA Finals.
Adrian Mannarino will face top seed Marco Cecchinato in the second round of the Kremlin Cup after ending a six-match losing streak by beating Evgeny Karlovskiy on Tuesday (AEDT).
Simona Halep will finish 2018 at the top of the WTA rankings, topping the year-end standings for the second consecutive season.
The luckless Juan Martin del Potro looks set to miss the ATP Finals after suffering a fracture to the patella of his right knee.
Dayana Yastremska completed a sensational week by claiming her maiden WTA Tour title with a 6-2 6-1 thrashing of Wang Qiang in Sunday's Hong Kong Open final.
China Open: Sevastova v Osaka