The PSV Eindhoven striker Ronaldo scored twice within seven minutes in the second half to set up Brazil's win after Ghana had taken a surprise 2-1 lead shortly after half-time.
His first goal was a simple shot after a quickly taken free-kick by Middlesbrough's Juninho, but the second showed all the class of a player bound for the glamour of Barcelona next season. The 19-year-old chipped goalkeeper Simon Addo from the tightest of angles to put Brazil 3-2 up 17 minutes into the second half.
Bebeto matched the subtle skills of his young compatriot with a fierce angled drive off a post to seal Brazil's victory in the 69th minute. Ghana had teenager Christian Sabah sent off in the 84th minute for a rash tackle on Ze Maria.
In Birmingham, Alabama, goals from Austin Okocha and Celestin Babayaro ensured Nigeria's progress to the semi-finals with a hard-fought win over Mexico.
Brazil and Nigeria, who play tomorrow in Athens, Georgia, will meet for the second time in a week. Brazil won their group match 1-0 in Miami last Thursday. Today's first semi-final in Athens is between Argentina and Portugal.
Wei Haiying scored twice in the final eight minutes to give China a 3- 2 victory over Brazil's women. The Chinese will play the United States for the gold medal on Thursday.Reuse content