Elina Svitolina and Aryna Sabalenka eased into the Silicon Valley Classic quarter-finals on a good day for the seeds.
Svitolina, the top seed at the WTA Premier event in San Jose, was untroubled by Daria Kasatkina in a 6-3 6-1 victory on Wednesday.
The Ukrainian is enjoying another fine year and her last-eight clash with Maria Sakkari will mark her sixth quarter-final of 2019 and she has won four of the previous five.
Sakkari, the seventh seed, was tested before getting past qualifier Mayo Hibi 4-6 6-4 6-2 at the hard-court tournament in California.
The second-seeded Sabalenka ended Coco Vandeweghe's first tournament of the year courtesy of a 6-3 6-3 victory.
Former world number nine Vandeweghe was making her return from ankle and foot injuries.
It was four from four for the seeds, with Carla Suarez Navarro beating Bethanie Mattek-Sands 3-6 6-1 6-2.
At the Citi Open, the only two seeds in action – Sofia Kenin and Monica Puig – departed.
Kenin went down to fellow American Lauren Davis 5-7 6-3 6-4 and Puig lost to qualifier Anna Kalinskaya 2-6 7-6 (7-5) 6-4.
Kristina Mladenovic edged 17-year-old wildcard Hailey Baptiste 6-4 4-6 6-3 and Jessica Pegula overcame Iga Swiatek 5-7 6-4 6-1.