Vera Zvonareva fended off Germany's Sabine Lisicki 6-3, 3-6, 6-4 on Friday to lead the top three seeds into the semi-finals of the WTA San Diego Open.
Fourth seed Peng Shuai of China was trying to make it four of the top four when she took on former Roland Garros champion Ana Ivanovic at the La Costa resort later Friday.
Top-seeded Zvonareva, twice a Grand Slam finalist in 2010, overcame six double-faults -- 12th-seeded Lisicki had nine -- to triumph in a tight match that lasted two and a quarter hours.
Russia's Zvonareva, who won a 12th career trophy last month in Azerbaijan, claimed her eighth consecutive match win to drive her record in 2011 to 28-6 on hardcourts.
Second-seeded Andrea Petkovic earned a win for Germany as she motored past US teenager Sloane Stephens 6-2, 6-1 in 66 minutes with minimal fuss.
Petkovic next faces third-seeded Agnieszka Radwanska, who shrugged off a sore right shoulder to beat eighth-seeded Daniela Hantuchova of Slovakia 0-6, 6-4, 6-4.
Radwanska admitted she entertained the idea of packing in the match after dropping the first set without winning a game, but pride steeled her to play on.
"You're playing Daniela, who is a great player. I could lose the match, but not 6-0, 6-0. I've been playing too well to lose so quickly," she said. "That pushed me to keep fighting."
Radwanska has been bothered by a nerve problem in her shoulder which has affected her serve. She was broken six times but still managed the win.
"Playing two hours is not really helpful for my shoulder, but I'll try my best tomorrow," said the Pole. "I didn't have much service, but I was just fighting till the end."
Petkovic. who has gone from strength to strength here as she launches her build-up to the US Open, schooled the 131st-ranked teenager with four breaks of serve as the youngster played in her first elite-level quarter-final.
"It's very important when you play these young players to show who's the boss on the court. There will come another time and another place when she will be a top player," said the winner.
The German is on track to break into the WTA Top 10 for the first time. She's projected to become the first German woman in the Top 10 in the world rankings since Anke Huber in October of 2000.