The fee for the youngster, who Chelsea have watched for the past two years, could rise to ?8million.
The 17-year-old Sao Paulo starlet is rated as one of the hottest prospects in Brazil and is representing his country at the Under 17 South American Championships.
Great expectations: Chelsea have high hopes for teenager Piazon
Piazon has drawn comparison to Kaka because the Real Madrid star also came through at Sao Paulo before heading to Europe, but the teenager is more of an out-an-out striker than his midfield senior.
The fee from Chelsea will help the Brazilian club pay for Luis Fabiano, the 30-year-old Tottenham target who snubbed a move to England to return home from Sevilla.
Piazon has scored twice in three games in Ecuador, a winning goal against Venezuela and a strike in a defeat against Paraguay that broke through the net.
He was the top scorer in the 2009 Under 15 South American Championship, hitting 10 goals - twice as many as his nearest rival - when Brazil finished runners-up behind Paraguay.
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