Fourth seed Thomaz Bellucci was a surprise loser in the first round of the Copa Claro as he was beaten by wildcard Diego Sebastian Schwartzman.
The Brazilian was defeated 6-4 4-6 6-1 in Buenos Aires by the Argentinian, who had never before won on the ATP tour.
A second homegrown player also progressed, with Federico Del Bonis seeing off Joao Sousa 6-1 6-4, but two more were bundled out.
Fifth seed Horacio Zeballos pushed hard but was defeated 4-6 7-6(4) 6-3 by Aljaz Bedene over Slovenia.
Spain's second seed Nicolas Almagro then eased into the next round with a 6-3 6-2 victory over Guido Pella.
Almagro's compatriot Albert Ramos, seeded eighth, beat Flavio Cipolla with ease in a 6-1 6-0 routing.
