World number two Dinara Safina battled into the fourth round of the WTA event in Indian Wells on Sunday, beating Peng Shuai of China 7-5, 6-4.
The Russian top seed, who will take over from Serena Williams at the top of the world rankings if she reaches the final this week, needed one hour, 48 minutes to see off Peng.
Safina will now play American Jill Craybas, a surprise 6-4, 6-3 winner over Czech Nicole Vaidisova.
"Today was strange," Safina admitted of the match against the 28th seeded Chinese.
"Normally [after] I [have] won the set, 7-5, I [should] be on a roll. Suddenly I stopped in the middle of the second set. I was like, 'what I'm doing? Just play'.
"Suddenly I started to be a little bit more aggressive."
Fourth seed Vera Zvonareva of Russia booked her place in the last 16 with a routine 6-3, 6-1 win over Czech Petra Kvitova.
Zvonareva will play China's Li Na, who upset former world number one Amelie Mauresmo of France 7-5, 6-2.
Eighth seed Victoria Azarenka of Belarus beat Elena Vesnina of Russia 6-3, 7-5, while ninth seed Caroline Wozniacki of Denmark advanced by beating Estonia's 18th-seed Kaia Kanepi 6-3, 3-6, 6-3.