The 21-year-old Pole upended 32nd-ranked Daniela Hantuchova of Slovakia 6-4, 7-5 on Day 1 of the California tournament.
Radwanska's older sister, Agnieszka Radwanska, won the event last year but is not defending her title.
Other winners Monday included American qualifier Alexa Glatch, Varvara Lepchenko of Russia and Japan's Misaki Doi.
The top seed at Carlsbad is Marion Bartoli of France.
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