Maria Sharapova was given a lukewarm welcome by 4,500 spectators upon her return to professional tennis on Wednesday after a 15-month doping ban.

After receiving a polite applause and some whistling when she entered the sold-out arena, the five-time Grand Slam champion and former No. 1 is playing Roberta Vinci in an opening-round match at the Porsche Grand Prix.

It's the Russian's first match since losing to Serena Williams in the quarterfinals of the 2016 Australian Open, and her first match on clay in nearly two years.

Last year, Sharapova tested positive for the banned substance meldonium. She had her initial two-year ban reduced to 15 months by the Court of Arbitration for Sport, which ruled that the Russian bore “less than significant fault” in the case and that she could not “be considered to be an intentional doper.”

Sharapova had been taking meldonium for many years, but overlooked an announcement by the World Anti-Doping Agency that it added the drug to its banned list on January 1, 2016.

Due to the suspension, Sharapova lost her ranking. But the three-time winner from 2012-14 was given direct entrance to the main draw of the Stuttgart event. Organisers in Madrid and Rome followed the example and handed her a wild card for their events in May as well.

Several players, including Vinci, have criticised the invitation for a player who has been caught doping.

Earlier on Wednesday, Sharapova completed a one-hour training session on an empty centre court.

Because her suspension ended only at midnight, she had not been allowed to use official tournament facilities before, forcing her to visit a local tennis club in Stuttgart for training since last weekend.