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 [Images] 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 [Images] of Russia [Images] 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 [Images] 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.