Ferrer fought off Tommy Robredo 6-3, 4-6, 6-0 and Almagro survived an even tougher match with Daniel Gimeno-Traver 7-6 (7-5), 4-6, 6-3.
Ferrer, seeded No. 1 here this year, won the title in 2007 with a victory over Almagro, the second seed. Almagro captured the event in 2010.
The quarterfinal opponent for Ferrer will be sixth-seed Grigor Dimitrov, who ousted No. 3 seed Albert Ramos 7-6 (7-1), 6-3.
Jan Hajek will take on Almagro after defeating Jurgen Zopp 6-3, 4-6, 6-3.
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