Sharapova was given a lukewarm welcome by 4,500 spectators upon her.
The Russian is yet to drop a set in her first three matches since returning from a 15-month doping ban this week, having been sanctioned after testing positive for meldonium at last year's Australian Open. Sharapova has also been granted wildcards into the Madrid and Rome WTA tournaments, but must wait until May 16 to learn if she will get a wild card for the French Open.
Maria Sharapova has no reply to Eugenie Bouchard's criticism that she should not be allowed back on the WTA Tour.
Five-time Grand Slam victor Sharapova's world ranking points expired during her suspension for testing positive for meldonium.
"It's so unfair to all the other players who do it the right way and are true".
"I don't. I'm way above that". 'I felt pretty good, and I think the adrenaline of just being excited and looking forward to competing and the challenge of every opponent, and the difference of play in each opponent, I'm mentally excited for it. It was not a prohibited drug prior to 2016.
There was no noticeable bad reception for the 30-year-old, who responded well to losing her first service game to take a tight opening set in Stuttgart. "I returned better today, but I know I can still improve that tremendously".
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After breaking when Sharapova served for the match, Kontaveit had the chance to level but Sharapova stepped up once more and took her first match point with a thumping return.
Should the Russian make the final she could break into the top 200, while a win in Germany would bump her up to around No125.
But the seven doubles were outweighed by nine aces, the last of them on her first match point.
With the win, Sharapova has now set up a second-round encounter against Russia's Ekaterina Makarova, who clinched a 6-2, 6-4 win over Polish star Agnieszka Radwanska.
"I am past "the lessons", I have done numerous interviews about the case and this is a new chapter in my career and that's how I want to move forward", she said.
Mladenovic ousted two-time defending champion Angelique Kerber on Thursday and is one of several players who has criticized Sharapova for her doping violation, but the Russian said she will not use it as added motivation in their semifinal on Saturday.