Radwanska, Sharapova land in Porsche quarters

Stuttgart, Germany ( - Top seed Agnieszka Radwanska and two-time defending champion Maria Sharapova were among Thursday's second-round winners at the $710,000 Porsche Tennis Grand Prix.

The Polish star Radwanska rolled past Italian Roberta Vinci 6-3, 6-2, while the sixth-seeded former world No. 1 Sharapova continued her winning ways in Stuttgart with a 6-4, 6-3 handling of fellow Russian Anastasia Pavlyuchenkova on the indoor red clay at Porsche Arena.

Radwanska and Sharapova will clash in Friday's quarterfinals. The Russian is a dominant 8-2 in their lifetime series, including a 2-0 mark on clay.

Sharapova beat Chinese stalwart Li Na in last year's marquee Porsche finale.

Upsets came when former Stuttgart champion Svetlana Kuznetsova vanquished second-seeded world No. 5 Romanian Simona Halep 7-5, 7-6 (7-4) and nifty Spaniard Carla Suarez Navarro cut down fourth-seeded German favorite Angelique Kerber 7-5, 6-4. The two-time major champion Kuznetsova captured this German event back in 2009.

Also, fifth-seeded former top-ranked Serbian star Jelena Jankovic came from behind to beat capable Italian Flavia Pennetta 3-6, 6-2, 6-3 and ninth-seeded former world No. 1 Serb Ana Ivanovic got past German wild card and 2011 Stuttgart champion Julia Goerges 1-6, 6-2, 6-1.

Jankovic, who was the Porsche titlist in 2009, will face Russian Alisa Kleybanova in the round of eight.

The other quarterfinals will pit eighth-seeded former French Open runner-up Sara Errani, of Italy, against Suarez Navarro and Ivanovic versus her fellow former French Open champ Kuznetsova.

The 2014 Stuttgart champ will claim $135,000 and a Porsche 911 Carrera sports car.