Sara Sorribes Tormo continued her good run of form in a surprise win over second seed Katerina Siniakova at the Copa Colsanitas, while Johanna Larsson and Lara Arruabarrena also reached the quarter-finals.
Spaniard Sorribes Tormo already has victories against Ekaterina Makarova, Eugenie Bouchard and Denisa Allertova this year and the unseeded 20-year-old added Siniakova to her list after triumphing 6-2 6-3 on Wednesday.
Sorribes Tormo reeled off six successive games as she came from a break down in the opening set before closing out the match with four of the last five games at the WTA tournament on the Colombian clay in Bogota.
Seeds Larsson, Arruabarrena and Magda Linette moved into the last eight with straight-set wins midweek.
Swedish third seed Larsson was too good for Veronica Cepede Royg 6-4 6-4, fourth seed and 2012 champion Arruabarrena saw off Irina Khromacheva 7-6 (7-3) 6-0, while fifth-seeded Pole accounted for Elitsa Kostova 6-4 6-4.
Sara Errani eliminated Sachia Vickery 6-2 6-3, Francesca Schiavone eased past Dalila Jakupovic 6-1 6-2 and Silvia Soler-Espinosa went down 6-0 7-5 to Aleksandra Krunic.