Cape Town - The ANC was leading the election with more than 11 million votes as counting neared the end on Friday, giving President Jacob Zuma a second term with a handful of fewer seats in Parliament.
The Democratic Alliance grew its vote share to 22% compared to the ANC's 62% and said the increase showed that it had managed to attract significantly more black supporters than before.
DA leader Helen Zille said one in five of the party's voters were now black.
"We grew our support among black South Africans from 0.8% in 2009 to approximately six percent in 2014," Zille said.
"Forty percent of these votes were won in Gauteng. This result shows that people's political attitudes are changing; that, more and more, people are moving away from race as a voting determinant."
The ANC held onto to its outright majority in the country's economic centre, taking 53% of the vote while the DA improved its vote share in Gauteng to 32%.
In the Western Cape, the DA surged to 59% after narrowly securing outright control of the province five years ago.
The party also became the official opposition in five more provinces, including KwaZulu-Natal.
Political analyst Richard Calland disagreed with the DA's assertion that it had made significant inroads among black voters, saying this was not even evident in the only province under their control.
"If they are to make progress nationally they have to build into working class areas and they have to start doing this in their home base here in the Cape," Calland said.
ANC ministers said the ruling party would use its fifth sweeping mandate to step up the pace of service delivery and infrastructure development over the next five years.
"It is no longer about celebrating - hard work lies ahead. We need to hit the ground running," said Public Enterprises Minister Malusi Gigaba, who is expected to remain in the Cabinet Zuma will announce in the next few weeks.
Against expectations of a significant stayaway to punish the ANC for its perceived excesses and failure to address economic inequality, the elections drew a turnout of more than 70%.
The ANC claimed its slimmest majority yet since Nelson Mandela led it to power in 1994, but defied predictions that it might sink below the 60% bar and will return to Parliament with only about four fewer seats.
The left-wing Economic Freedom Fighters are set to stride into Parliament after claiming just more than six percent of the vote - which should translate into 23 seats in the legislature.
Agang, after its aborted merger with the DA, secured only 49 000 votes in the election and could narrowly secure a single seat.
Calland said it remained to be seen whether Mamphela Ramphele would take up the seat or quit politics after a disastrous run.
Zille was scathing of the woman she had invited to stand as the DA's presidential candidate.
"Mamphela has destroyed her political brand and value," she told reporters.
The Electoral Commission of SA (IEC) said after a slow start counting in Gauteng was some 95% complete on Friday afternoon and confirmed that it would release the official national results at 18:00 on Saturday.
IEC chairperson Pansy Tlakula said the commission had taken its time in hotly contested areas, such as that province, to make sure its results were accurate.
The African Union election observer mission on Friday declared the vote free and fair, and praised the commission's use of technology.
"The preliminary conclusion is that the elections were free, fair and transparent," said head of the AU observer mission, Professor Ibrahima Fall.
"The process was elaborate to ensure accountability," he said.