After trading holds with fellow German Dinah Pfizenmaier, the fourth-seeded Petkovic reeled off five straight games to win the first set. She cruised to a 4-1 lead in a second set in which she would break serve three times and went on to a 6-1, 6-3 triumph.
"I was focused from the very beginning," Petkovic said. "That doesn't happen often; at Wimbledon, I started badly in every match. But today I played well throughout the whole match."
While she is 7-7 on hardcourts and 3-2 on grass this year, Petkovic is 16-5 on clay - highlighted by the biggest WTA title of her career in Charleston and her first Grand Slam semifinal at Roland Garros.
Petkovic is no stranger to success on the red clay of Bad Gastein, having captured her maiden WTA title here in 2009.
"I feel very good on the court here once I get used to the high altitude after a couple of matches," Petkovic said. "It suits my game very well."
"Stefanie is a very good player," said Petkovic, who is 3-1 in her head-to-head with the Swiss. "We had a very tough match in Roland Garros. She hits the ball early and has a strong serve. I need to be aggressive and serve just as well, and then we'll see what happens."
Petkovic also commented on Germany's World Cup semifinal rout of Brazil on Tuesday.
"I just watched the first half, but I was already feeling bad for Brazil," Petkovic said. "A 4-1 win would have been enough, but I'm very happy that Germany advanced to the final."
Setting up a quarterfinal with victories over qualifiers were eighth-seeded Karolina Pliskova and Grace Min. Pliskova beat Ana Bogdan, 6-2, 7-5, and Min secured her first WTA quarterfinal berth by defeating fellow American Irina Falconi, 6-3, 6-3.