Second-ranked Maria Sharapova began her clay court season on Wednesday by reaching the quarterfinals of the Porsche Grand Prix when her opponent Alize Cornet of France retired with a shoulder injury.
The Russian was leading 6-3, 1-0 when qualifier Cornet quit because of the right shoulder injury.
Caroline Wozniacki of Denmark advanced to the second round when Jelena Jankovic of Serbia also retired with an identical score of 6-3, 1-0 in Wozniacki's favor.
Mona Barthel of Germany saved three set points and rallied to upset Ana Ivanovic of Serbia 7-5, 7-6 (4) in another first-round match.
Ivanovic led 5-3 in the first set and held three set points on Barthel's serve. But the German wild card saved two and then fired an ace to turn the match around.
Agkul Amanmuradova of Uzbekistan replaced the injured Daniela Hantuchova in the main draw and went on to upset another Slovak, Dominika Cibulkova, 6-2, 5-7, 6-3.
Fourth-seeded Agnieszka Radwanska of Poland cruised past qualifier Greta Arn of Hungary 6-3, 6-4 to reach the quarterfinals.