Brazil won 1-0 over Peru at the Centenario, but it took 80 minutes before Demitrinho could strike.
The Peruvian defence defended like dogs until Demitrinho's hopeful strike from long range caught out the keeper.
Brazil now book a place in the knockout stages.
In the day's early game, Ecuador were held 1-1 by Canada.
Marco Giontarella had given the North Americans a shock lead, before Luis Martini equalised fifteen minutes from time.
On Monday, Ecuador, with one point, could qualify for the quarters if they beat Peru in Maldonado, who are currently on three, and Canada are still in the hunt if they complete the unlikely task of beating Brazil at the Centenario, coupled with a draw in the other game in Maldonado. However if Peru beat Ecuador no matter what happens in Montevideo, they will go through with Brazil.
