Two-time champ Robredo falls to Ramos in Stockholm
The fourth-seeded Robredo didn't reach a break point against Ramos.
Grigor Dimitrov rallied to beat Filippo Volandri 2-6, 6-1, 6-4. Dimitrov also recovered from a set down in his first-round win against Elias Ymer.
Argentines Juan Monaco and Carlos Berlocq earned spots in the quarterfinals after beating Henri Laaksonen and Blaz Kavcic, respectively.
Tomas Berdych and Nicolas Almagro will begin play on Thursday.