The Czech Republic's Lucie Safarova upset No. 4 seed Dominika Cibulkova, of Slovakia, 7-6 (7-5), 6-1 in the round of 16 at the Miami Open in Key Biscayne, Florida.
The 30-year-old Safarova, the 2015 French Open finalist, hit 28 winners in the match, while Cibulkova, the world No. 4, had only 11 winners in the match.
Safarova, the world No. 36, had a 2-5 career record against the 27-year-old Cibulkova heading into the match at the Crandon Park Tennis Center.
Cibulkova struggled with her service game, hitting on just 60 percent of first serves and 28 percent on second serves.
The Slovakian star converted on only one of seven break opportunities against Safarova.
Safarova's quarterfinal opponent will be the winner of the match between Spain's Garbiñe Muguruza and Denmark's Caroline Wozniacki.
Safarova, the finalist in Budapest last month, and Muguruza have only played two times, splitting the wins.
The two last played at the 2015 French Open, where Safarova knocked off Muguruza 7-6 (7-3), 6-3 in the quarterfinals.
American Serena Williams defeated Safarova 6-3, 6-7 (2-7), 6-2 in the final for her third French Open title.