The Spaniard, sixth-seeded in the tournament on Seoul's Olympic Park hard courts, showed her experience in both tiebreaks and won her fifth career title and second this year.
Both players earned one service break each in the first set, but Martinez Sanchez dominated the tiebreak without giving up a point.
Voskoboeva, in her first WTA singles final, bounced back and took a 3-1 lead in the second set but was unable to hold her serve.
Martinez Sanchez, ranked No. 36, again took control in the tiebreak to defeat the No. 82-ranked Voskoboeva, who became increasingly frustrated.