The 12th-ranked Haas served well throughout the match at the Ibirapuera arena, allowing only one break point to the 152nd-ranked Italian.
Both players held serve until the first-set tiebreak, when Haas stepped up his game to easily clinch the set. The German then broke Starace's serve two times in a row late in the second set to close out the match in 1 hour, 30 minutes.
"It's my first match ever here, the conditions are tough, the ball flies pretty hard," the 35-year-old Haas said. "My opponent played through qualifying and won his first round-match. He has a lot of kick on his serve so I was trying to get some rhythm. I was able to hold my serve quite comfortably, which was nice. I played a pretty good tie break."
Haas will next play Argentina's Horacio Zeballos, who defeated countryman Guido Pella 6-3, 6-4.
"(He is) a very good clay-court player, also a lefty, which makes him a little bit stronger," said Haas, who had a bye into the second round. "So it's going to be tough."
Second-seeded Nicolas Almagro of Spain, a three-time winner in Brazil, was upset by Federico Delbonis of Argentina 6-3, 3-6, 2-6. The 17th-ranked Almagro had 10 break points but only capitalized in one of them, in the first set.
"I have to look ahead, it's a long year and it's just beginning," Almagro said. "I didn't play at my best level but I know that I can do a lot better."
The 61st-ranked Delbonis had never advanced past the qualifying round in his four appearances at the Brazil Open. He will play his quarterfinal against Albert Montanes of Spain, who advanced when Brazilian Joao Souza retired with back problems while trailing 6-4, 2-3.
"I wasn't able to serve," Souza said. "There was nothing I could do. I'm sorry for the fans."
Defending champion Rafael Nadal, who won the Rio Open last week, is not playing at Sao Paulo this year.
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