Seeded 3rd Dementieva, who won the Kremlin Cup in 2007, fought a tough two and a half hour match against her compatriot Nadezhda Petrova to snatch a tie-break victory in the third set 6-4, 4-6, 7-6 (8-6).
Later in the day Zvonareva (7) enjoyed a straight sets victory over Dominika Cibulkova of Slovakia in a match which lasted an hour and 40 minutes and ended 7-5, 6-4 in favor of the Russian.
Dementieva will now face in the semifinals the winner of the quarterfinal match between Jelena Jankovic of Serbia and Flavia Pennetta of Italy, while Zvonareva is set to meet either Svetlana Kuznetsova or Dinara Safina who play later today.
The tournament prize money in the women's singles is some $1.34 million, while the men's singles competition has $1.05 million up for grabs.
The Kremlin Cup, held this year for the 19th time, was Russia's first international professional tournament and is one of the richest events in the ATP's (Association of Tennis Professionals) International Series.
