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Wilfredo Lee, Associated Press
A tennis fan seeks shelter from the hot sun as they watch a match between Victoria Azarenka of Belarus, and Michaella Krajicek of the Netherlands, during the Sony Ericsson Open tennis tournament, Friday, March 23, 2012, in Key Biscayne, Fla.

KEY BISCAYNE, Fla. — Top-ranked Victoria Azarenka extended her winning streak to 24 matches Friday by beating Michaella Krajicek 6-3, 7-5 in the second round at the Sony Ericsson Open.

Azarenka's streak began with her first match this year, and her start is the best since Martina Hingis went 37-0 to begin 1997. Azarenka is bidding for her third Key Biscayne title and second in a row.

No. 15-seeded Ana Ivanovic lost only six points on her first serve and beat American Vania King 6-4, 7-5. Ivanovic was playing for the first time since she retired with a left hip injury a week ago at the Indian Wells semifinals.

Two wild cards eliminated seeded women. Garbine Muguruza Blanco of Spain upset No. 9 Vera Zvonareva 6-4, 6-3, and Aleksandra Wozniak of Canada rallied past No. 28 Monica Niculescu 4-6, 6-3, 6-4.

No. 18 Angelique Kerber lost to Zheng Jie 7-6 (4), 6-1. No. 31 Kaia Kanepi was beaten by Silvia Soler-Espinosa 7-5, 6-3.

On the men's side, No. 4 Andy Murray won his opening match by beating Alejandro Falla 6-2, 6-3.

Murray, the 2009 champion, bounced back from a loss in his first match at Indian Wells two weeks ago. He also avoided a repeat of last year, when he lost his opening match at both Indian Wells and Key Biscayne.

With the victory, Murray improved to 15-3 this year.

Other seeded men to reach the third round included No. 6 Jo-Wilfried Tsonga, No. 9 Janko Tipsarevic, No. 13 Gilles Simon, No. 18 Alexandr Dolgopolov and No. 22 Jurgen Melzer.

Azarenka double-faulted six times and lost three service games, but Krajicek was even more erratic with her serve. Krajicek failed to hold at 5-4 in the second set, double-faulting three times, and Azarenka swept the final 10 points.

The Belarussian seeks her fifth title this year. She won Indian Wells a week ago.