Brazil took the lead when a cross from the right by striker Robinho, who seemed to be in an offside position when he received the ball from Kaka, was turned into his own net from close range by Keith Andrews one minute before halftime.
Substitute Daniel Alves should have doubled the lead after the break when he rounded Ireland keeper Shay Given and shot wide of the empty net.
Robinho, who ended an unhappy spell with Manchester City by returning home to join former club Santos on loan in January, added a second on 76 minutes with a neat side-footed finish following a quick passing move involving Kaka and Grafite.
"Robinho is someone who has always had big emotion for the national team and he was decisive today," Brazil coach Dunga told reporters.
"Sometimes people ... talk bad about him. Everybody can go through a good or a bad moment but ... certain players are very important to us and the whole team has to be behind those players."
Ireland matched Brazil in the first half but the South Americans were completely on top in the second period, with Robinho and Kaka combining particularly well.
The only blot on the evening for Robinho came in the second half when he spooned a chance over the bar from eight metres after another flowing move down the right.
Brazil begin their World Cup challenge when they face Group G rivals North Korea in Johannesburg on June 15. They then face Ivory Coast five days later and Portugal on June 25.
Ireland were playing their first game since their World Cup qualification dreams ended in despair in November when France claimed a controversial playoff victory.
"For 45 minutes we saw a very beautiful game," said Ireland coach Giovanni Trapattoni. "I think we played at the same level as Brazil.
"I thought in this moment we could also hope ... for a good result (but) the first goal was offside by one metre," added the Italian.
