The world's top-ranked women's player needed just over an hour to beat Martinez Sanchez on Monday for the first time in four meetings. Wozniacki has improved her results in each of her first four years playing at Indian Wells, where she was runner-up to champion Jelena Jankovic last year.
There were two upsets on the men's side: fourth-seeded Robin Soderling of Sweden and No. 11 seed Nicolas Almagro of Spain both lost.
Soderling fell to No. 32 seed Philipp Kohlschreiber of Germany, 7-6 (8), 6-4; while 23rd-seeded Albert Montanes of Spain took out Almagro 4-6, 6-2, 6-4.
Other women's winners were No. 9 Agnieszka Radwanska of Poland and No. 22 Alisa Kleybanova of Russia.
Later Monday, top-seeded Rafael Nadel played American qualifer Ryan Sweeting and Maria Sharapova faced Aravane Rezai of France.
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