On Friday, she produced arguably her best performance since returning from four months out with an ankle injury to dismiss No.1 seed Nina Bratchikova in under an hour.
Looking to build on a promising run to the semifinals in Luxembourg, Petkovic, whose injury woes have seen her plummet from the Top 10 to No.143, accepted a wildcard for the WTA $125 event last week. And, after struggling in her opening match, Petkovic has looked every inch the Top 10 player in the last two rounds.
While Petkovic was a picture of focus and consistency throughout, Bratchikova's game never clicked into gear, setting the tone with an error-strewn opening game to drop serve. The German broke serve again in the fifth game to wrap up the set before moving through the gears in the second, romping home, 62 60.
"Sometimes when you play a really tough opponent, something just clicks in your mind and that's what happened today," Petkovic said. "The score looks easy, but against very good players, like Nina, things can change in a minute and I knew that I cannot afford to relax against her.
"I was very consistent and really on my top level the whole match - I am very happy the way I played."
Next, Petkovic faces Elina Svitolina, whose opponent Luksika Kumkhum retired midway through their quarterfinal. Having lost the first set on a tie-break, Svitolina was 4-1 ahead in the second when a rib injury forced Kumkhum to retire.
Date-Krumm played some of her best tennis of the year to defeat fellow Japanese player and No.2 seed Misaki Doi, 61 64.
Doi was not even born when Date-Krumm turned professional back in 1989, but she had no answer to the spins and angles conjured up by her opponent, who won the final three games to wrap up victory after just one hour and 15 minutes.
"Today was mentally very tough," Date-Krumm said. "She has improved so much this year and it's also tough to play another player from Japan. I think it was difficult for her too and I could tell she was getting nervous at the end of the second set.
"I was pretty tired after all my matches this week, so I'm very happy it was over in just two sets!"
Tanasugarn made an inauspicious start to her match with high-flying Donna Vekic, falling an early service break behind. However, she came roaring back to take the next six games before staging a similar recovery in the second to defeat her shell-shocked teenage foe, 62 64.