Officials called for a truck to be parked alongside the pitch after the lights went out at the Engenheiro Araripe stadium, allowing the players to practice ahead of Thursday's friendly against Nigeria.
The match is being played in Espirito Santo, a small coastal state where no games were held during the 2014 World Cup. Brazil built or renovated 12 stadiums for the competition.
Rafinha Alcantara (Barcelona), Andreas Pereira (Manchester United) and Felipe Anderson (Lazio) are among the biggest names in a squad that will try to win Olympic gold for the first time in August in Rio de Janeiro.
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(Writing by Andrew Downie; Editing by Peter Rutherford)
