Massu will face sixth-seeded Nicolas Almagro of Spain in the clay-court event.
Almagro beat Italy's Filippo Volandri 6-3, 6-3 to reach his third straight quarterfinal. Almagro won his third career title in Brazil, then retired because of a groin injury while leading in the quarterfinals last week in Buenos Aires.
"Yesterday I served 13 aces, today 12. I'm happy, working a lot in all of the facets of my tennis," Almagro said.
Top-seeded David Nalbandian, the Argentine star coming off a victory Sunday in Buenos Aires, routed Spain's Santiago Ventura 6-2, 6-3. Nalbandian will face eighth-seeded Potito Starace, the Italian who beat Australia's Peter Luczak 6-3, 6-3.
Canas apologized to countryman Carlos Berlocq, whom he beat on Tuesday. Berlocq asked for a doctor to check a stomach pain during their second set, and Canas called Berlocq's behavior "trash."
"Those comments came in the heat of the moment, while leaving the court," Canas said on Wednesday. "When one is mad one can make comments that shouldn't be made."
"I push myself very hard. ... It was a good game but not an incredible game," Pennetta said. "The important thing was to win and go on."
Second-seeded Alize Cornet of France beat Mexico's
Melissa Torres Sandoval 6-2, 6-0. Third-seeded Klara Zakopalova of the Czech Republic, the runner-up in Vina del Mar to Pennetta just over a week ago, dropped a 6-1, 4-6, 7-6 (2) decision to American Jill Craybas.