Coco Gauff defeated home favourite Katerina Siniakova in straight sets to advance to the second round of the Ostrava Open.
Teenager Gauff, who made the main draw after a pair of wins in qualifying, fought back from a break down three times in the opening set and went on to triumph 7-5 6-4.
A meeting with third seed Aryna Sabalenka is the next task for the American, who has won just two of her past seven matches on the WTA Tour.
Elena Rybakina has reached a Tour-leading five finals in 2020 but the eighth seed fell to a 6-2 3-6 6-3 defeat to the measured Daria Kasatkina.
Kasatkina played an intelligent, efficient match and had 15 winners to 14 unforced errors, while Rybakina had 35 to 49.
Veronika Kudermetova's 6-2 6-4 victory over Donna Vekic booked a second-round meeting with Karolina Pliskova, while there were also wins for Jennifer Brady and Ons Jabbeur.
