Tunisia's Ons Jabeur will play Russian Daria Kasatkina in the final of the Kremlin Cup in Moscow after knocking out Latvia's Anastasija Sevastova.
The WTA's season climax will feature eight top-ranked players except world No.1 Simona Halep, who has been forced to withdraw through a back injury.
Australian ace Nick Kyrgios has withdrawn from the Kremlin Cup with an elbow injury with his opponent Mirza Basic given a free ticket to the quarter-finals.
Former US Open champion Samantha Stosur concedes her time on the WTA tour is nearing an end as she enters her 21st season on the circuit.
Nick Kyrgios has battled his way to a three-set win against Russian Andrey Rublev at the Kremlin Cup while Daria Gavrilova advanced in the women's draw.
Twin brothers and Ukrainian tennis players Gleb and Vadim Alekseenko have been banned for life after committing multiple match-fixing offences.
The Kremlin Cup campaign of Australian Ajla Tomljanovic is over after a straight-sets defeat to Russian Anastasia Pavlyuchenkova.
Simona Halep ends 2018 again as the WTA's world No.1 for the second year in a row but doctors fear a back injury cause long-term issues.