Del Potro, the No. 1 seed this week, raced past seventh-seeded Albert Montanes 6-2, 6-2. He did lose his serve once in each set but easily countered that with six breaks over the eight games Montanes served.
Joining del Potro in Saturday's semifinals are second-seeded Richard Gasquet, No. 3 Stanislas Wawrinka and fourth-seeded Albert Ramos.
Gasquet topped Daniel Munoz-de la Nava 7-6 (7-1), 6-2, dropping just four points on serve in the second set.
Also Friday, Wawrinka eliminated Robin Haase 6-1, 6-4 in 58 minutes and Ramos beat Joao Sousa 6-2, 6-3 without dropping serve.
Del Potro takes on Wawrinka in the semifinals. They have split their four previous meetings. Gasquet and Ramos are 1-1 against each other, with both matches this year and going three sets.