Two-time defending champion and top-seeded David Ferrer of Spain defeated Santiago Giraldo of Colombia 6-4, 7-6 (1) Thursday to reach the quarterfinals of the Copa Claro clay-court tournament.
Ferrer has won 20 times on the ATP tour and is a strong favorite to make it three straight in the Argentine capital.
Fourth-seeded Nicolas Almagro also reached the quarterfinals, defeating fellow Spaniard Daniel Gimeno-Traver 1-6, 7-5, 6-4.
Almagro has won all of his 12 ATP titles on clay - six in Latin America - and could face Ferrer in the semifinals.
Eighth-seeded Jeremy Chardy of France joined Almagro and Ferrer in the quarters, defeating Alexandr Dolgopolov of Ukraine 6-3, 3-6, 7-6 (3).
Second-seeded Fabio Fognini of Italy reached the final eight on Wednesday, as did No. 3 Tommy Robredo of Spain.