Zhang Shuai and CiCi Bellis booked their spots in the Hawaii Open quarter-finals on a good day for the seeds.
Zhang, the top seed at the WTA 125K series event, overcame Marina Erakovic 7-5 6-3 in the second round on Thursday.
All five seeds in action advanced, with Bellis - the talented 17-year-old American - easing past countrywoman and fellow teenager Usue Maitane Arconada 6-1 6-2.
Samantha Crawford, Evgeniya Rodina and Sara Sorribes Tormo also won through.
Crawford beat Danielle Collins 6-1 7-5, Rodina was too good for Katie Swan in a 6-2 6-3 win and Sorribes Tormo fought her way past Asia Muhammad 6-3 4-6 6-1.
The day's other match saw Sachia Vickery ease past Eri Hozumi 6-4 6-1.