Wimbledon champion Petra Kvitova was upset by Alexandra Dulgheru in the first round of the U.S. Open on Monday.

The 48th-ranked Romanian won 7-6 (3), 6-3. The fifth-seeded Kvitova committed 52 unforced errors.

Dulgheru improved to 3-9 against top-10 opponents, with her first victory on a surface other than clay. She had played only one singles match since Wimbledon because of injuries to both knees.