Second seed Vera Zvonareva came from behind to beat Russian Fed Cup team-mate Anastasia Pavlyuchenkova and book her place in the last eight at Stuttgart's WTA tournament on Wednesday.
The 26-year-old Zvonareva, ranked third in the world, recovered from losing the first set to seal a 3-6, 6-4, 6-2 win over Pavlyuchenkova, 19, who was also part of the Russian team that white-washed champions Italy 5-0 in Moscow last weekend.
Zvonareva admitted she was not surprised to have lost the opening set as she struggled to cope with her first appearance of the year on clay.
She increased her confidence as the two-hour match wore on, however, before blasting down three aces in the third set.
Zvonareva now faces Australia's Samantha Stosur or Slovakian Daniela Hantuchova in Thursday's quarter-finals.
"She's good, we'll be seeing more of her in the future," said Zvonareva of her teenage opponent, who is on the verge of breaking into the world's top 20.
"It was my first game on clay this season, so I just hung in there.
"Last week I was practising with her a lot, but it is totally different in a match situation. It was hard to go out and play her, but it's part of the job."
Zvonareva said she is looking forward to getting in some clay-court practice here ahead of next month's French Open.
"I have been injured for the last couple of clay-court seasons. I know I can play well on the surface, I just need to get some practice in," she said.
There were shocks as French eighth seed Marion Bartoli and Italy's third seed Francesca Schiavone both went out.
Bartoli suffered the biggest upset as she was beaten in straight sets 6-4, 6-2 by German wild-card Kristina Barrois in just 85 minutes.
The German belied her ranking of 79th in the world to blast four aces down at her French opponent, ranked 12th in the world, who hit four double faults.
Barrios will face Poland's Agnieszka Radwanska in Thursday's quarter-finals after she put out Schiavone with an impressive 6-1, 6-3 victory.
"This is a huge success, because I was the complete outsider," said Barrois. "I have nothing to lose again now (against Radwanska).
"My mother is very ill, things are getting increasingly difficult at home, but every victory helps of course. I am lucky I have a big family."