Kremlin Cup
Fourth seed Anastasia Myskina kept up her recent good form with victory over Magui Serna in Moscow.
The Russian swept into the last eight with a 6-3 6-1 win over the Spaniard.
Myskina came into the tournament on a high having beaten Justine Henin-Hardenne at last week's Sparkassen Cup.
"My recent wins over top-ranked players at Leipzig filled me with confidence and I realised I can play and beat them," said Myskina.
Eleni Daniilidou of Greece will be Myskina's quarter-final opponent after beating Tina Pisnik 6-3 3-6 6-4.
Myskina was joined in the last eight by fellow Russian Vera Zvonereva, who saw off compatriot Vera Douchevina 6-2 6-2.
And third seed Elena Dementieva, currently the world number eight, also made it through, eliminating qualifier
Jelena Kostanic of Croatia 6-2 6-3.
It was not a complete rout for the home players, however, as Italian Francesca Schiavone beat Dinara Safina 7-5 7-6.
Japan Open
Top seed Ai Sugiyama was forced to pull out of her quarter-final with Aniko Kapros because of a finger injury.
The Japanese player trailed 6-4 3-2 when she decided that an injury to her left ring finger was too painful for her to continue.
Sixth seed Ashley Harkleroad suffered a surprise 7-6 6-4 defeat to China's Yan Zi.
But Russian teenager Maria Sharapova, seeded fifth, had no problem against Japan's Akiko Morigami, winning 6-1 6-3 to move into the last eight.