Defending men's champion Viktor Troicki and top-seeded woman Vera Zvonareva advanced to the quarterfinals of the Kremlin Cup with straight-set victories on Wednesday.
The second-seeded Troicki beat Pere Riba of Spain 6-4, 6-4, while Zvonareva routed Bojana Jovanovski of Serbia, 6-1, 6-1.
Also Wednesday, Kaia Kanepi of Estonia came from 5-1 down in a third-set tiebreaker to upset fourth-seeded Francesca Schiavone of Italy 6-4, 5-7, 7-6 (7).
Troicki broke once in each set and sealed the victory on his first match point. The Serbian player will face Alex Bogomolov Jr. of the United States, who beat his doubles partner Mikhail Kukushkin of Kazakhstan 6-4, 3-6, 6-4 to advance.
"It was a tough match today," Troicki said. "It was tough to break him. He was serving always over 200 (kph). But I also served good."
Last year, Troicki beat Marcos Baghdatis of Cyprus in Moscow for his first career title.
"I hope to do well to defend my title, but there's a lot of good players and I still have three matches to go to defend it," Troicki said.
The fifth-seeded Bogomolov Jr. broke his opponent once in the first set to take the lead, but stumbled in the second set, losing four games in a row at one point. He saved two break points before breaking Kukushkin in the third game of the decisive third set, and held on to win.
Bogomolov Jr., who was born in Moscow, is making his debut at the event.
Zvonareva, runner-up here in 2008, won nine consecutive games before Jovanovski held her serve in the fourth game of the second set. The Russian went on to finish the match in just over an hour.
"From the stands the matched looked like an easy one," Zvonareva said. "But there were tough games in which I managed to stay concentrated. I didn't make consecutive unforced errors and didn't allow her to feel as if she was leading the play. And it was the key to my victory."
The Russian, who has not played a competitive match since losing in the second round in Beijing two weeks ago, is using the tournament to prepare for next week's season-ending WTA Tour championships in Istanbul.
Second-seeded Agnieszka Radwanska, who was scheduled to face Lucie Safarova later Wednesday, can secure the last spot with a victory.
In the last two women's first-round matches, eighth-seeded Dominika Cibulkova of Slovakia defeated Polona Hercog of Slovenia 6-3, 7-6 (3), while Elena Vesnina routed wild card Alla Kudryavtseva 6-0, 6-1.