Petkovic sets up German duel with Kerber in Stuttgart

Berlin - Angelique Kerber will face compatriot Andrea Petkovic in the second round of this week's WTA tournament in Stuttgart, after Petkovic beat Spain's Sara Sorribes Tormo in straight sets on Tuesday. 

World number five Kerber was granted a bye to the second round after Simona Halep withdrew from the tournament with an injury, and will now face her friend and compatriot in an all-German duel on Thursday.

"I am looking forward to playing Angie, not just because she is a friend, but also because it will be a great challenge," said Petkovic after beating Tormo 6-3, 6-4 on Tuesday. 

In the other ties Belgium's Greet Minnens sprung a surprise when she beat Slovakian Dominika Cibulkova, ranked 159 places above her, to set up a second round meeting with world number three Petra Kvitova. 

Laura Siegemund became the third German to reach the second round when she beat Ukrainian Lesia Tsurenko, while Anna-Lena Friedsam went down fighting in two sets against Dutch sixth seed Kiki Bertens.

Earlier in the day, Elise Mertens of Belgium was knocked out by Russia's Darya Kasatkina, and Anastasika Sevastova overcame fellow Latvian Jelena Ostapenko in a rollercoaster battle over three sets.