KEY BISCAYNE, Fla. (AP) -- In a nature preserve across the street from the Sony Ericsson Open, waterfowl trade calls not unlike the shrill shrieks heard on stadium court Friday afternoon.

Defending champion Victoria Azarenka was back in action on Key Biscayne. The noisiest No. 1 since Maria Sharapova, Azarenka hooted with nearly every stroke and won her opening match over Michaella Krajicek, 6-3, 7-5.

It was the Belarrussian's 24th victory in a row. The streak began with her first match this year, and her start is the best since Martina Hingis went 37-0 in early 1997.

"I'm not really thinking about numbers, the streaks, whatever,'' Azarenka said. "It's your job to count; mine is to play tennis.''

There were no questions at a postmatch news conference about Azarenka's grunting. She dislikes discussing the subject, and her record of late says it all anyway.

Azarenka won her first Grand Slam title in January at the Australian Open, where she beat Sharapova in a shriekers' showdown to earn the No. 1 ranking. She also has won titles this year at Sydney, Doha, and - just a week ago - Indian Wells.

When asked to give a reason for the streak, Azarenka wavered.

"There is not really an answer,'' she said. "There is one thing that I do, and it keeps happening for me: to win. There is really no magic.''

Bidding for her third Key Biscayne title, Azarenka was joined in the third round by 15th-seeded Ana Ivanovic, who 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 was far from sharp against Krajicek, double-faulting six times and losing 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.

When Azarenka put away an overhead for 5-all, Krajicek angrily flung her racket against the backstop, and a linesman hopped to avoid getting hit.

With Krajicek in meltdown mode, Azarenka took advantage and swept the final 10 points.

"It was important to raise my level at the end of the match,'' Azarenka said. "I found the right shot selection and the right opportunities when I needed to.''

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