Azarenka was leading 6-2, 4-4 when the German stepped awkwardly and twisted her right ankle on the indoor red clay court. Petkovic didn't even try to continue playing and had to be helped off the court.
Ranked No. 11 in the world, Petkovic was in the second match of her comeback after injuring her lower back in January. Petkovic was the first German woman to finish a year in the top 10 since Steffi Graf in 1998.
Barthel has jumped from No. 196 to 35 in the past year. She had seven aces against Bartoli and dominated with her powerful game.
Li Na of China topped Agkul Amanmuradova of Uzbekistan 6-4, 6-4.