Ronaldo on target in Corinthians win
The 2002 World Cup winner swept the ball home in the 26th minute to notch his fifth goal for the club after the Ituano defence was caught out by a quickly-taken free kick.
Corinthians had taken the lead with a Jorge Henrique header in the second minute and went further ahead when midfielder Cristian scored from a free kick four minutes before halftime.
The win kept Corinthians second in the table and guaranteed them a place in the semi-finals of the Paulista, the biggest of the regional tournaments which kick off the Brazilian season.
Leaders Palmeiras were held to a 1-1 draw at Oeste, who went ahead when Ademar chipped the ball over Marcos early in the second half.
Vanderlei Luxemburgo's team levelled when Mauricio Ramos headed in from Cleiton Xavier in the 70th minute.