The Polish world number four needed just 62 minutes to wrap up victory against the Spaniard who is ranked 104th in the world.
Radwanska has dropped only seven games in her two matches in the tournament.
Next up for Radwanska is a clash against Russia's Vera Dushevina.
Second seed in the tournament Maria Kirilenko was defeated by 42-year-old Japanese veteran Kimiko Date-Krumm, who will now face former French Open champion Francesca Schiavone in the last eight.
After the match Kirilenko revealed she had picked up an injury and would miss next week's WTA Tokyo event.
Results from the Seoul Open Women's Singles Round 2 matches on Thursday
1-Agnieszka Radwanska (Poland) beat Estrella Cabeza Candela (Spain) 6-2 6-1
Jang Su-Jeong (South Korea) beat Ons Jabeur (Tunisia) 1-6 6-4 6-1
Kimiko Date-Krumm (Japan) beat 2-Maria Kirilenko (Russia) 6-3 6-1
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- Maria Kirilenko