INDIAN WELLS, California:, March 18, 2009 (AFP) - Victoria Azarenka stunned top-seeded Russian Dinara Safina 6-7 (4/7), 6-1, 6-3 Wednesday to book a semi-final berth at the Indian Wells hardcourt tennis tournament.

The 19-year-old from Belarus, seeded eighth, denied Safina's latest bid to seize the world number one ranking from Serena Williams, who is idle this week.

Safina could have supplanted the American, who beat her in the Australian Open final, by reaching the final here.

But in Azarenka, she ran into a player brimming with confidence after capturing her first two career WTA titles this year - in Brisbane and Memphis.

Safina appeared to have the match in her grasp when she took a 3-1 lead in the third set, but she couldn't hold on to the lead.

Azarenka notched her first victory over Safina in four career meetings.

In the semi-finals, Azarenka will face her doubles partner, fourth-seeded Russian Vera Zvonareva, a 6-4, 6-2 winner over Denmark's Caroline Wozniacki.

Currently at No.6 in the standings, Zvonareva has one title to her credit already this year, at Pattaya City.

A break in the third game was all Zvonareva needed to win the first set. She broke her 18-year-old opponent three times in the second to secure the victory.

Zvonareva won the last five games of the second set, but had to fight off break points in both the fourth and sixth games.

Quarter-finals in the bottom half of the draw are scheduled for Thursday, when defending champion Ana Ivanovic, the fifth seed, takes on Sybille Bammer of Austria and seventh-seeded Pole Agnieszka Radwanska plays 17-year-old Russian Anastasia Pavlyuchenkova.

The second-round exits of second-seeded Jelena Jankovic and third-seeded Elena Dementieva left Zvonareva is the top seed remaining in the field.