Azarenka will face in-form Mona Barthel of Germany for a place in the last four after Germany's
Azarenka grabbed a break in the opening game but missed an easy volley to hand it back in the fourth game to Petkovic, who had only this week returned to the Tour after almost four months out with a back injury.
She then proceeded to break the German again to take the first set 6-2.
The second set initially followed a similar pattern with Azarenka breaking in the first game courtesy of a stunning double-handed backhand down the line before being broken straight back.
World number 12 Petkovic looked set to give her opponent a tougher time but badly twisted her ankle as she tried to hit a forehand at 4-4 with the indoor crowd instantly falling deadly quiet.
"It's such a tough situation and the ankle right away blew up," said Azarenka.
"I hope she recovers soon because she is a great player. Andrea is one if the players who is tough mentally, she is a great fighter," she said.
"It was one of the best matches of my life," said Barthel, who won her maiden WTA title in Hobart in January. "I was immediately able to put her serve under pressure. It's great to have won my first match against a top 10 player. It's something special."
World number five
German Kerber also caused a major upset, dismantling former world number one Wozniacki 6-1 6-2 to set up a mouth-watering clash with Wimbledon champion
The Czech advanced with a comfortable straight-sets victory over Italy's