Elena Rybakina completed a clean sweep of her group at the WTA Finals with a straightforward victory over late call-up Ekaterina Alexandrova.
The sixth seed, who sealed her progression to the semi-finals on Monday, continued her momentum with a 6-4 6-4 win in Riyadh.
The Kazakh had been due to play Madison Keys, but the American - who could not advance - withdrew just hours before the start of the match because of illness.
Alexandrova was the second alternate, but received the nod after fellow Russian and first option Mirra Andreeva, who is also competing in the doubles in Riyadh, declared she was not fit to play.