Barthel exits Stuttgart

Stuttgart, Germany ( - Monday's lone main draw match saw wild card Carina Witthoeft dismiss fellow German Mona Barthel 7-5, 6-3 at the Porsche Tennis Grand Prix.

Opening-round action will come Tuesday for fifth-seeded former world No. 1 Ana Ivanovic, sixth-seeded Russian left-hander Ekaterina Makarova and eighth- seeded Spaniard Carla Suarez Navarro on the indoor clay at Porsche Arena.

The top seeds at this star-studded tournament are French Open champion Maria Sharapova, French Open runner-up Simona Halep, Wimbledon titlist Petra Kvitova and U.S. Open runner-up Caroline Wozniacki.

The former world No. 1 Sharapova is the reigning three-time Porsche champ, having beaten Ivanovic in last year's marquee finale.

The former top-ranked star Wozniacki was a finalist here back in 2011.

The 2015 Stuttgart champion will earn $108,000 and a new Porsche 911 Carrera sports car.