PORTOROZ, Slovenia -- Croatian teen Petra Martic upset former champion Klara Zakopalova 6-3, 4-6, 7-6 (3) on Wednesday to reach the Slovenia Open quarterfinals in her second WTA Tour event.
The victory by 17-year-old Martic, ranked 237th, was her first over a top 100 player.
Zakopalova won the inaugural Portoroz title in 2005.
Martic broke into the top 300 only on Monday, a day after winning a satellite event, the Zagreb Open. She then beat Angelique Kerber of Germany in the first round for her first win on the main tour. In the quarterfinals, she could face either second-seeded Katerina Srebotnik or Julia Goerges of Germany.
In other second-round matches, third-seeded Caroline Wozniacki of Denmark rolled past wild card Karolina Sprem of Croatia 6-1, 6-1; fourth-seeded Anabel Medina Garrigues of Spain topped Julia Vakulenko of Ukraine 6-4, 6-4; and Vera Dushevina of Russia beat Katie O'Brien of Britain 6-3, 6-2.