Saint Petersburg - Second seed Kiki Bertens of the Netherlands eased into the Saint Petersburg WTA indoor last eight by brushing aside Belgian qualifier Ysaline Bonaventure on Thursday.

Bertens, who is ranked eighth in the world, fired 13 aces to see off the left-handed Bonaventure 6-4, 6-2 in one hour to record her third win over the 24-year-old in as many meetings and to chalk up her first ever in Russia.

"I've never won before in any tournaments that were held in Russia and I'm really happy to win today," Bertens said.

"It's always difficult to play against left-handed opponents but today I played well, especially in the first set when my serve was working really good."

The 27-year-old Dutchwoman will next meet Russia's Anastasia Pavlyuchenkova, who upset sixth-seeded former French Open champion Jelena Ostapenko of Latvia 6-4, 6-4.

Aryna Sabalenka of Belarus, seeded fourth, also cruised into the last eight with a straight-sets win over another Belgian player Alison Van Uytvanck 6-1, 6-4.    

Sabalenka will next face Ekaterina Alexandrova of Russia who outgunned Czech Tereza Martincova 7-5, 6-2 in a battle of qualifiers.

Results from the Saint Petersburg WTA tournament on Thursday (x denotes seeding):

2nd rd

Ekaterina Alexandrova (RUS) bt Tereza Martincova (CZE) 7-5, 6-2

Aryna Sabalenka (BLR x4) bt Alison Van Uytvanck (BEL) 6-1, 6-4

Anastasia Pavlyuchenkova (RUS) bt Jelena Ostapenko (LAT x6) 6-4, 6-4

Kiki Bertens (NED x2) bt Ysaline Bonaventure (BEL) 6-4, 6-2