Sharapova - the seventh seed from Russia - had few problems in reaching her first semi-final at Roland Garros since losing to Ana Ivanovic in 2007.
Petkovic failed to collect a game in the opening set as she was broken three times. She clawed her way back to some sort of respectability by trading breaks with Sharapova in the second set, but lost the final three games of the match to crash out in straight sets.
Sharpova is bidding to the French Open for the first time having won Wimbledon in 2004, the US Open in 2006 and the Australian Open three years ago.
Sharapova, the most experienced woman left in the draw with a title at each of the other three grand slams, has been hampered by injuries and illness since.
A slow start to the second grand slam of the season became a shrewd bid at peaking at the right time for the seventh seed once the top three seeds crashed out early.
Now the Russian, who has wowed the galleries with the same shade of fashionable dress each match and even came on court with a trendy handbag, is taking the tournament even more seriously with her first French Open title in sight.
Dogged defending champion Francesca Schiavone or French crowd favourite Marion Bartoli await in Saturday's final, but Sharapova must first negotiate a passage past fighter Li Na.
"I don't remember the last time we played but I'm very excited to be in the semi-finals," Sharapova said courtside when asked about her 2009 last-16 win over Li on the Paris clay. China's Li completed a 7-5 6-2 win over Victoria Azarenka.