Almagro, the top seed, didn't allow a single break point to Hanescu in his victory at the Ibirapuera sporting complex. He had 12 aces and only one double fault in the second-round match that lasted more than two hours.
"I played well but I know that I can improve, I have confidence in my game," Almagro said. "Victor took advantage of his chances in the second set, but in general it was positive, I didn't have any break points against me."
The 11th-ranked Almagro needed a wild card to defend his title because he initially wasn't certain if he would make the tournament because of his Davis Cup duties with Spain. He also won the Brazil Open in 2008.
"I kept focused from the beginning, that was key, it made everything easier," Nalbandian said.
Third-seeded Fernando Verdasco of Spain struggled against countryman Javier Marti but escaped with a 6-4, 6-7 (2), 7-5 victory after saving triple match points against the 20-year-old Marti. Verdasco, a former No. 7 in the world who was playing his first match since the Australian Open, had six double faults, including four in the final set.
Also, fifth-seeded Carlos Berlocq of Argentina defeated Potito Starace of Italy 3-6, 6-2, 6-3, converting five of the 13 break points he got in the nearly two-hour match. Eighth-seeded Albert Ramos of Spain ousted big-server Igor Andreev of Russia 7-6 (4), 7-6 (4).
Almagro will face Berlocq in the quarterfinals, while Verdasco will play Ramos. Homecrowd favorite Thomaz Bellucci will play Mayer and Nalbandian will face Volandri.
The indoor clay-court ATP 250 event is being played in South America's biggest city for the first time after 11 editions in the northeastern city of Costa do Sauipe.