Former champion Victoria Azarenka was ousted by Barbora Krejcikova while fifth seed Maria Sakkari fell to Jessica Pegula in the Australian Open fourth round.
Azarenka, who won the title in 2012 and 2013, fell to French Open winner Krejcikova 6-2 6-2.
Greece's Sakkari was beaten 7-6 (7-0) 6-3 by former semi-finalist Pegula.
Madison Keys continued her strong form with victory over Spanish eighth seed Paula Badosa.
Keys will face Krejcikova next, while Pegula will face either top seed Ashleigh Barty or American compatriot Amanda Anisimova.
Azarenka's exit means that Rafael Nadal is the only former Australian Open champion remaining in either the men's or the women's draw.