Led by top-seed David Ferrer of Spain, seeded players had an easy day on Tuesday as almost all moved through to the second round of the clay-court Copa Claro.
Ferrer had no trouble beating Argentine Andres Molteni 6-1, 6-0.
"I'm happy to get out of the first round, and I think he (Molteni) was a little nervous," Ferrer said.
Molteni had plenty of support from local fans, who were hoping for some revenge for Spain's victory over Argentina last year in the Davis Cup final at Seville, Spain.
"I like fans supporting the local players," Ferrer said. "It's the normal thing to do, and personally I like it."
No. 2 Nicolas Almagro of Spain advanced against Potito Starace of Italy 4-6, 6-3, 7-6 (4), and No. 3 Gilles Simon of France defeated Rui Machado of Portugal 6-3, 7-5.
No. 5 Juan Monaco of Argentina moved on when Filippo Volandri of Italy retired in the second set with an injury. Monaco was leading 6-1, 3-1.
Seventh-seeded Fernando Verdasco of Spain also reached the next round, beating Eric Prodon of France 6-4, 6-1.
The biggest upset came when eighth-seeded Juan Ignacio Chela of Argentina lost to Albert Ramos of Spain 4-6, 6-3, 6-4.
Home favorite David Nalbandian defeated Wayne Odesnik of the United States, 6-2, 6-3.
"Always playing at home is special," Nalbandian said. "It was a little windy out there today and the ball was moving around a bit."
In other matches, Benoit Paire of France defeated Javier Marti of Spain 2-6, 7-6 (0), 6-2, Igor Andreev of Russia won over Blaz Kavcic of Slovenia 6-2, 6-2 and Federico Delbonis of Argentina defeated Frederico Gil of Portugal, 6-2, 6-2.