One person died when a tree fell on an outdoor stall, authorities said. At least six other people in surrounding Sao Paulo state also died.
Authorities originally expected to restore power within a few hours. But several neighborhoods in the metropolitan area, which is home to 21 million people, were still in the dark on Saturday, and authorities were urging residents to limit their consumption of water.
Most of the disruptions were in the service area of a single utility, Enel-Sao Paulo.
Regulators ordered an inspection of the utility, warning that if it doesn't resolve the outages in a satisfactory and swift manner it will move to terminate the private concession.
For its part, Enel said that 17 high voltage transmission lines were affected by the storm. It did not provide a time frame for re-establishing service.