Madison Keys reached the third round of the Volvo Car Open after a hard-fought victory over Lara Arruabarrena.
The American, who was runner-up at the event in Charleston three years ago, beat Spain's Arruabarrena 6-1 3-6 6-3.
After easing through the first set, the seventh seed was made to work in the final two sets but ultimately prevailed with six aces and 35 winners after one hour and 38 minutes on court.
She will next face Camila Giorgi, with the Italian a 6-2 2-6 6-3 winner over 11th seed Daria Gavrilova of Australia.
There were also upsets that saw second seed Petra Kvitova and Britain's Johanna Konta bow out.
Kvitova could not maintain a strong start, losing 1-6 6-1 6-3 to Kristyna Pliskova, while sixth seed Konta suffered a 6-3 6-4 defeat at the hands of world number 219 Fanny Stollar.
Wild card Sara Errani fought back to beat 15th seed Mihaela Buzarnescu 3-6 7-6 (7/5) 6-2, while 12th seed Kiki Bertens was a 6-4 6-2 winner over Kiki Bertens, France's Alize Cornet triumphed 6-2 6-3 against Polona Hercog and Julia Goerges - seeded number five - came back from a first-set setback to beat Kristie Ahn 2-6 6-4 7-6 (7/1).
There were also wins for eighth seed Anastasija Sevastova, Naomi Osaka, Elena Vesnina, Ashleigh Barty, Bernarda Pera and Irina-Camelia Begu.
