The Korea Open draw was blown wide open by the second-round departure of leading seeds Kiki Bertens and Kristyna Pliskova on Tuesday.
Bertens, seeded second, suffered a 5-7 6-4 6-3 loss to fellow Dutchwoman Richel Hogenkamp, while third seed Pliskova went down 6-4 6-4 against world number 274 Han Na-lae.
Top seed Jelena Ostapenko's relatively serene progress stood in stark contrast to her rivals' woes, the Latvian prevailing 7-6 (8-6) 6-1 over Johanna Larsson.
With reigning champion Lara Arruabarrena having already exited, the title is very much up for grabs for all the remaining contenders.
But eighth seed Christina McHale is not among them after she too fell in round two, Arantxa Rus claiming a 6-3 6-4 win.
Elsewhere in the draw, there were straight-sets victories for Nao Hibino, Denisa Allertova, Veronica Cepede Royg and Nicole Gibbs.