Australian top seed Samantha Stosur earned a quarter-final spot at the Kremlin Cup with a straight-sets win over France's Alize Cornet on Thursday.
In the men's section, French qualifier Edouard Roger-Vasselin produced a big upset as he survived four match points before seeing off Ukraine's top seed Alexander Dolgopolov in a tough third-set tiebreak.
Stosur, who is ninth in the WTA rankings, prevailed 7-6 (8/6), 7-5 in two hours 28 minutes to draw her head-to-head record with the 22-year-old Cornet level at 2-2.
"We always play tough against each other," Stosur said. "But we haven't met for a long time and we have both seriously improved our tennis since our last meeting."
"Today I had plenty of opportunities and chances to finish the points off. And it was important to believe I was doing everything right to receive the win as a reward."
The rivals traded breaks twice in the opening set to force a tiebreak which Stosur won to gain a one-set lead in one hour 21 minutes.
In the second set there was little between the pair but the 28-year-old Stosur got the deciding break in the 11th game to take the set and the match.
Stosur will now face Czech Klara Zakopalova for a place in the semis.
Fourth seed Ana Ivanovic of Serbia cruised comfortably into the last eight with a 6-1, 6-4 win over 19-year-old local qualifier Valeria Solovieva.
"It was a good match for me overall," the 2008 French Open champion and former world number one Ivanovic said.
"Though the surface here is rather slow and it took some time to adjust to it.
"And it's never easy to play someone you haven't seen before as you don't know how they react in the different situations but I'm happy I managed to finish the match in good style."
Seventh seed Maria Kirilenko, the last Russian player in the field, beat Yaroslava Shvedova of Kazakhstan 7-5, 6-4 on her way into the quarter-finals.
Roger-Vasselin, 116th in the ATP rankings, advanced into the quarter-finals with a 6-3, 5-7, 7-6 (8/6) win over Dolgopolov and next faces Croatian giant Ivo Karlovic, who ousted Alex Bogomolov of Russia, for a place in the last four.
"It was a very close and tough match. And it was decided by just a couple of points," the 28-year-old unheralded Frenchman said.
"I survived four match points but also missed several easy shots before winning the match."
"I didn't play yet against Karlovic but it's going to be a really tough quarter-final match anyway."
Italy's second seed Andreas Seppi beat Dutchman Igor Sijsling 7-5, 6-2 to meet eighth seed Tatsuma Ito in a match for a place in the semis.
Argentina's seventh-seeded Carlos Berlocq missed out on the quarter-finals, suffering a 6-3, 6-4 defeat to unheralded Pole Jerzy Janowicz, who is 74th in the ATP rankings.