Elena Rybakina stunned Iga Swiatek to confirm her place in the knockout stages of the WTA Finals while Amanda Anisimova produced a comeback victory to stay in contention in Riyadh.
Former Wimbledon champion Rybakina was outplayed in the opening set against world number two Swiatek but completely dominated thereafter.
Sixth seed Rybakina won 12 of the final 13 games to storm to a 3-6 6-1 6-0 win and snap a four-match losing streak against Swiatek.
American Anisimova later beat Madison Keys to send Rybakina through to the semi-finals.
"Mentally, I am happy that I stayed focused.