Li Na, Petra Kvitova lead Stuttgart quarterfinalists

Seeded players Li Na, Angelique Kerber and Petra Kvitova advanced to the quarterfinals of the Porsche Grand Prix on Thursday. Second-seeded Li swept past

Seeded players Li Na, Angelique Kerber and Petra Kvitova advanced to the quarterfinals of the Porsche Grand Prix on Thursday.

Second-seeded Li swept past qualifier Mirjana Lucic-Baroni 6-1, 6-2, and the third-seeded Kerber defeated Anastasia Pavlyuchenkova 6-0, 6-4.

Fifth-seeded Kvitova rallied past 2011 champion Julia Goerges 2-6, 7-6 (4), 6-2. Kvitova, the 2011 Wimbledon champion, is aiming for her second title of the year.

Ana Ivanovic beat eighth-seeded Nadia Petrova 6-4, 6-3. One day after upsetting Caroline Wozniacki, Carla Suarez Navarro lost 7-5, 6-4 to Yaroslava Shvedova.