Brazil cruised past Cameroon to open their Group E campaign with a victory in the women's football competition.
Jorge Barcellos's team raced into a 2-0 lead through a Francielle free-kick and a header from Renata Costa.
Marta scored a second-half penalty after she had been clumsily fouled by Bebey Beyene before Cristiane slotted home from a tight angle.
The losing Olympic finalists in 2004 and 2008 made it 5-0 late on when Marta struck from close range.
The match was the second of a double header at the Millennium Stadium in Cardiff after Great Britain had earlier opened their campaign with a 1-0 win over New Zealand.
And the emphatic nature of Brazil's victory ensures that they finish the opening day of Olympic action top of their group on goal difference.
It might have been even more emphatic but Ester shot wide in the opening half and impressive substitute Cristiane missed with a spectacular over-head kick close to the final whistle.
Cameroon were second best throughout the contest, and especially overrun in the latter stages, with a completely unmarked Marta given the freedom of the six-yard box to pick her spot for Brazil's fifth.
However, Cameroon did come close to a goal shortly before half-time when Gabrielle Onguene created an opening with a neat run and turn but she then shot wide.