Three-times champion Kim Clijsters battled past Jelena Jankovic 5-7, 6-2, 6-2 in the second round of the Bank of the West Classic in Stanford on Wednesday.
The top seed was joined in the quarter-finals by French teenager Tatiana Golovin who enjoyed a 6-2, 6-3 upset win over sixth-seeded Ai Sugiyama, and Australian Samantha Stosur who toppled seventh seed Shahar Peer of Israel 7-5, 6-3.
Russian Vera Zvonareva won a repeat of last week's Cincinnati final by taking down eighth seed Katarina Srebotnik 6-4, 6-3.
She will next meet experienced Frenchwoman Nathalie Dechy, who overcame Italy's Maria Elena Camerin 0-6, 7-6, 6-3.
Playing her first match since leading Belgium to a Fed Cup semi-final victory over the US, Clijsters produced erratic tennis but wore down the hard-hitting Jankovic in long rallies.
After blowing a 5-3 lead in the first set, the US Open champion jumped on her opponent in the second, hammering her forehand and mixing up balls from her backhand side.
Clijsters saved three break points early in the third set and broke the 27th-ranked Jankovic to 4-2 when her opponent doubled faulted.
Clijsters fought off four break points in the next game and after Jankovic lost a video replay challenge on game point, she collapsed, losing the match in the next game on a backhand error.
"Even when you are not playing your best you have to hang in there mentally," Clijsters told reporters. "In the long rallies, I was able to defend well and I felt I was moving well. I was happy about that."
Jankovic was 1-4 in replay challenges and at one point in the first set, asked the fans whether she should use one.
"The said yes, challenge it, and of course they were wrong," Jankovic said. "It was really unfortunate."
In the first three days of the tournament, players have challenged 24 calls and have only overturned four of them.
Golovin won her fourth consecutive match over Sugiyama and feels nearly recovered from an ankle injury sustained in March.
"I have a few more tournaments left before the US Open and it's just a matter of playing more and recovering from the ankle," she said. "I'm just trying to get back to where I was at the beginning of the year."
Jill Craybas took down fellow American Shenay Perry 6-3, 3-6, 7-6 to reach the quarter-finals.
Japanese qualifier Akiko Morigami continued her run by beating 33rd-ranked Gisela Dulko of Argentina 6-0, 6-3.
