(CNN) -- Women's world number one Victoria Azarenka is through to the third round of the Miami Masters, extending her winning run in 2012 to 24 matches after beating Michaella Krajicek of the Netherlands in straight sets.
Azarenka has already won four tournaments in an astonishing start to the year and the Belarusian was expected to brush past her 71st-ranked opponent.
But Krajicek had other ideas, battling all the way before Azarenka's superior quality finally told in a 6-3 7-5 victory that took one hour and 42 minutes.
However, there were plenty of shock results elsewhere in the women's draw, with ninth seed Vera Zvonareva the biggest casualty, the Russian going down 6-4 6-3 to Spanish wild card Garbine Muguruza Blanco.
Also departing the tournament are 18th seed Angelique Kerber, Lucie Safarova (27), Kaia Kanepi (31) and Nadia Petrova (32), who all lost in straight sets, while Monica Niculescu (28) was beaten in three.
But 15th seed Ana Ivanovic is through after seeing off American Vania King 6-4 7-5, while fifth seed Agnieszka Radwanska, 16th seed Dominika Cibulkova and 22nd seed Maria Kirilenko also advanced in straight sets.
They were joined in the last 32 by Italian Flavia Pennetta, but the 24th seed was taken to three sets by Lourdes Dominguez Lino of Spain before prevailing.
Meanwhile, in the men's draw, fourth seed Andy Murray secured his place in the last 32 with a routine 6-2 6-3 win over Alejandro Falla.
The Briton's 76-minute victory ended a losing run on the Florida hardcourts which had seen him beaten in his opening matches in both 2010 and 2011.
There were also straight sets win for seeds Jo-Wilfried Tsonga (6), Janko Tipsarevic (9), Gilles Simon (13), Alexander Dolgopolov (18), Florian Mayer (19) and Philipp Kohlschreiber (32), while 22nd-seeded Austrian Jurgen Melzer went through in three sets.