Top seed Francesca Schiavone of Italy, winner of the French Open, suffered a second round exit at the Istanbul WTA tournament in Istanbul on Thursday.
The world number eight lost to Britain's Elena Baltacha 6-4, 6-2.
"She served very well and played well at the most important moments," the 30-year-old Shiavone said.
"I didn't play so well so I'm a little bit upset, but it can happen," she added.
"I'm really proud. It's my third top 10 win and I've had such a great year," said Baltacha, the world number 59.
"I'd like to think this is the real Elena Baltacha. I'm beginning to perform much more consistently, and I'm improving a lot. I still have a few things to work on but I feel every week I'm adding a lot of positives," she said.
Baltacha was the first British woman to beat a top 10 player in over a decade. Her first top 10 wins came this year - beating Li Na at Indian Wells and Eastbourne.
"In the three weeks off after Wimbledon, one of the things I worked on with my coach was trying to expose my opponent then run around and finish with a forehand," said Baltacha.
Baltacha will face German sixth seed Andrea Petkovic for a place in the semifinals.