The Russian’s presence at the tournament has triggered controversy after she was handed a wildcard to participate in the tournament because her ranking expired in the 15 month suspension she had for doping violations.
Sharapova says she has grown in confidence during her strong start at the tournament.
She faces Estonian Anett Kontaveit on Friday.
World number two ranked Angelique Kerber was knocked out of the Stuttgart Open in the round of 16 on Thursday by French woman Kristina Mladenovic – 19th in the world.
The German struggled in the first set which ended 6-2 in Mladenovic’s favour.
The pair battled out a tight second set which saw Mladenovic break Kerber in the final game to take the game 6-2 7-5. Mladenovic faces Carla Suarez Navarro in the quarter-finals on Friday.