China's Zheng Jie capitalised on a final set meltdown by world number one Dinara Safina to reach the quarter-finals of the LA Championships with a 7-5, 4-6, 6-4 victory over the Russian on Thursday.
The 14th seeded Zheng stood strong against a barrage of huge blows from her opponent over the course of the two hour, 10 minute contest to emerge with a first win in five attempts against the defending champion.
"It's tough to play her but I didn't do the right things," Safina told reporters. "I should have played better. She took her chances and beat me."
Zheng advanced to a last eight encounter against in-form Australian Samantha Stosur, who continued her fine season with a 6-3, 6-2 victory over sixth seed Ana Ivanovic.
The 13th seed was delighted to overcome the Serbian former world number one, gaining some revenge for losing to Ivanovic in their last meeting at Wimbledon in June. It was also Stosur's sixth win over a top 15 opponent this year.
"Anytime you play against someone you lost to recently, it's a bit of a benchmark to test yourself," Stosur said.
Russia's Maria Sharapova continued her rehabilitation from a lengthy injury layoff when she rallied from a set down to defeat Alona Bondarenko 4-6, 6-0, 6-3.
The three-time grand slam champion benefited from a more aggressive approach against the Ukrainian compared to the last time they met in May, a straight sets victory for Bondarenko in Sharapova's first tournament back from shoulder surgery.
"It was good to get the win and get my revenge," the unseeded Sharapova said.
"I actually thought I was physically fresher than her in the third set. It gives me a lot of confidence that I can step it up when I need to especially after losing to her a few months ago."
Sharapova will face Polish teenager Urszula Radwanska, who advanced when 12th seed Li Na of China withdrew due to a right ankle injury.
Second seed Vera Zvonareva also advanced with a 7-6, 4-6, 6-4 win over Yanina Wickmayer of Belgium and the Russian moves on to meet 10th seed Flavia Pennetta of Italy, who upended Nadia Petrova 6-3, 6-3.
Number eight seed Agnieszka Radwanska, Urszula's older sister, eased past Russia's Anna Chakvetadze 6-3, 6-2 and will play Sorana Cirstea of Romania, who was 6-3, 1-0 ahead of Sabine Lisicki when the German retired with a right shoulder injury.