"South Africans remembered their combined power, switched off and achieved a massive 629MW average reduction on their electricity usage," said Eskom in a statement.
The power utility said the savings took place during Earth Hour between 8.30 and 9.30 on Saturday night.
Last year, South Africans reduced their energy usage by approximately 402MW during earth hour – enough electricity to power Bloemfontein.
"This year's figure shows that more and more South Africans are seeing the value of switching off what they are not using."
On Saturday, Public Enterprise Minister Malusi Gigaba warned South Africans to brace themselves for what could be the most difficult winter "as electricity supply remained constrained".
"We need to worry about how we are going to go through this winter," Gigaba told residents in Kliptown, Soweto.
Earth Hour started in 2007 in Sydney, Australia, when private households and businesses turned off their lights for an hour to take a stand against climate change.
Starting with Sydney
On Saturday, Mail & Guardian reported that Sydney kicked off the event at 8.30 pm, cutting lights to cheers and applause from a small crowd who had gathered to see the skyline dim and Sydney Opera House turn a deep green to symbolise renewable energy.
Organisers expected hundreds of millions of people across more than 150 countries to turn off their lights for 60 minutes on Saturday night, in a symbolic show of support for the planet.
Japan switched off soon after Australia, with the illumination on the landmark Tokyo Tower dimming down as visitors were given the chance to pedal bicycles to generate power to illuminate an egg-shaped artwork.
Last year more than 150 countries participated in the event which saw some of the world's most iconic landmarks dim, and this year the movement has spread to Palestine, Tunisia, Suriname and Rwanda.
Newcomers that plunged into darkness included Copenhagen's Little Mermaid, the statue of David in Florence and Cape Town's Table Mountain. – Sapa