Russian Qualifier Vitalia Diatchenko upset top seeded Dominika Cibulkova to setup an all-Russian quarterfinals match against sixth seeded Anastasia Pavlyuchenkova at the Kremlin Cup in Moscow on Thursday.

The 24-year-old Diatchenko dropped the first set but rallied 10 of 11 points to win the second set.

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With momentum on her side, Diatchenko built a 4-0 lead in the third and deciding set. After that, the players kept breaking each other until the Russian came out on top 4-6 6-2 6-2 in a match that lasted just under two hours.

This is Diatchenko's first win over a top 50 player where Cibulkova is ranked World No. 14.

With Cibulkova's loss, second seeded Ekaterina Makarova of Russian, who also lost her opening round has clinched the second alternate position at the season-ending WTA Finals in Singapore. Angelique Kerber is the first alternate.

The WTA decided to include a second alternate this year as three players are nursing injuries. Serena Williams has a left knee injury, Eugenie Bouchard has a left thigh injury and Ana Ivanovic has a hip injury. If two of the players mentioned could not participate, then Kerber and Makarova will take their place.

Diatchenko will now face sixth seeded Anastasia Pavlyuchenkova in an all-Russian encounter.

Pavlyuchenkova defeated last week's inaugural Tianjin Open champion Alison Riske in two straight sets 6-2 6-2 in 59 minutes.

The Open GDF Suez champion Pavlyuchenkova dished out nine service aces and connected six of 12 break points to end the American's winning streak.

In the other side of the top half, third seeded Flavia Pennetta was also upset by fellow compatriot Camila Giorgi in an all-Italian second round 7(7)-6(4) 6-4.

Girogi, 22, will go up against a surprise player in Katerina Siniakova, an 18-year-old qualifier from the Czech Republic.

Siniakova has yet to drop a set in the tournament as she defeated veteran Elena Vesnina, Makarova's partner in the doubles competition, 6-2 6-2 in the first round and Kristina Mladenovic of France 6-1 6-1 in the second round which lasted just 58 minutes.

Tagsdominika cibulkova, Vitalia Diatchenko, Anastasia Pavlyuchenkova, Katerina Siniakova