Arruabarrena-Vecino won 84 percent of her first-service points and was 3-for-4 on break points in her efficient 6-3, 6-4 victory over Brazilian Teliana Pereira.
Sixth-seeded Elina Svitolina of Ukraine moved on to the semis with a 6-3, 7-5 win over Mariana Duque-Marino of Colombia in a match lasting 70 minutes.
The semifinals field was rounded out by Colombia's Catalina Castano, who beat Sesil Karatancheva of Khazakstan in three sets, and Paula Ormaecheva of Argentina, who also needed three sets to upset No. 4 seed Alexandra Panova of Russia.
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