Caroline Wozniacki advanced to the quarterfinals of the Kremlin Cup on Wednesday by beating Urszula Radwanska of Poland 6-1, 6-3.
Sofia Arvidsson of Sweden upset second-seeded Marion Bartoli 6-3, 6-0 in the second round.
The third-seeded Wozniacki won five consecutive games in the first set and broke Radwanska twice in the second to take a 5-2 lead. She lost four match points trying to serve out the match and Radwanska broke to stay in the contest. But the Pole sent a forehand wide in the next game to hand Wozniacki the victory. The Dane is looking for her second title of the year and 20th of her career.
She will play defending champion Dominika Cibulkova of Slovakia, who advanced to the final eight with a 6-2, 6-3 win over Tsvetana Pironkova of Bulgaria.
Arvidsson broke Bartoli three times and dropped serve twice in the first set. The Frenchwoman had six double-faults in the second set.
Arvidsson, who won her second career title in Memphis this year, will face either seventh-seeded Maria Kirilenko or Yaroslava Shvedova of Kazakhstan.
"I am very happy to win this match to reach the quarterfinals," Arvidsson said. "Marion is a great competitor, a top-10 player, and I knew I would have to be at my best. My strategy was to focus on the way I wanted to play and move her around the court."
The result means the 10th-ranked Bartoli can't overtake No. 9 Samantha Stosur and will remain the second alternate at the season-ending WTA Championships next week in Istanbul.
"Of course it would have been better for me to come to Istanbul as the first substitute, but it's always very rewarding for me to get a chance to go there," Bartoli said. "Today my body just refused to execute what my mind was telling it to do. The surface here is very slow and it didn't fit my play well."
Klara Zakopalova advanced to the final eight by defeating eighth-seeded Lucie Safarova 6-4, 6-4 in all-Czech match, while Valeria Solovieva of Russia moved into the second round by downing Elina Svitolina of Ukraine 6-4, 6-2.
In first-round action, Kirilenko topped fellow Russian Elena Vesnina 7-5, 6-1.
In men's second-round play, Malek Jaziri of Tunisia upset the third-seeded 2010 champion Viktor Troicki of Serbia 6-1, 3-6, 6-2.
Eighth-seeded Tatsuma Ito of Japan defeated Russian qualifier Konstantin Kravchuk7-6 (7), 2-6, 6-3, while Lukas Rosol of the Czech Republic rallied past fifth-seeded Denis Istomin of Uzbekistan 4-6, 6-4, 6-3.