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Lisicki, seeded No.1 this week for the first time in her career, shook off a second set lapse and jumped out to a two-break, 3-0 third set lead in edging Barthel, 76(3) 36 63.
"I improved from my last match, which I knew I had to do, but I still didn't play consistently enough to win in two sets," said Lisicki, who will play fellow German Angelique Kerber in Thursday's quarterfinals. "But then again the most important thing when you don't play your best tennis is to find a way to win. We're working on a couple of things. I'm still improving."
Kerber was one of five unseeded players to take down a seed Wednesday, as she recorded a 62 63 victory over No.5 seed Julia Goerges. Also, Lucie Hradecka downed No.2 seed Peng Shuai, 64 63, Elena Vesnina eliminated No.6 seed Roberta Vinci, 63 64, Sara Errani was a 46 61 61 winner over No.7 seed and 2010 Auckland champion Yanina Wickmayer, and Zheng Jie routed No.8 seed Monica Niculescu, 60 62.
The two seeds besides Lisicki to advance were third-seeded Svetlana Kuznetsova and fourth-seeded Flavia Pennetta. Kuznetsova got her first win in three career tries over Christina McHale, 61 61, and has just dropped seven games through two matches this week. Next up for her is Errani. Pennetta defeated Elena Baltacha, 64 62, and will square off with Vesnina.
"It was a good match. I was ready for a fight," Pennetta said. "I feel better than the first day here. It's the first tournament of the year and it's not easy to be consistent all the time, but we're all in the same situation."