There are more than 4,700 delegates attending the conference just outside Johannesburg which got off to a late start due to disputes over which delegates are qualified to vote, and further challenges may be lodged.
The two leading contenders, Cyril Ramaphosa and Nkosazana Dlamini-Zuma, were seen embracing and sharing a light-hearted moment during the gala dinner.
Political analyst Tinyiko Maluleke says the exclusion of 54 provincial executive committee members and 40 Bojanala branches from voting will not adversely affect Dlamini-Zuma's fortunes.
Zuma, who has led the ANC since 2007, will step down as party boss at the end of the conference.
In opposition, the Democratic Alliance and the Economic Freedom Fighters are hoping to exploit the ANC's woes in the 2019 election, with one possible outcome being a coalition government. "You can not afford to lose delegates, especially in the climate where the momentum has been shifting away from NDZ towards Cyril Ramaphosa", political analyst Aubrey Matshiqi said.
He promised to write his biography in a year, and promised to always be ready for deployment should the incoming leadership call on him. "Whether it is enough is another question", said Matshiqi. The new ANC president is likely to become the country's next president. The Saturday night endorsement of Ramaphosa by Baleka Mbete, the party's outgoing national chairwoman and a Zuma ally, has fueled speculation that the race may be swinging in the deputy president's favor.
Asked whether she thought Zuma was "a nice guy to work with", Dlamini said he was "an ordinary man who is the president of the ANC who has at all times, even hard times, calmed down".
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"We publicly endorse comrade Cyril Ramaphosa", she told reporters after Saturday's opening session at the conference.
Zuma said he always believed the job was a serious task.
Dlamini-Zuma, 68, headed the African Union commission until earlier this year and is a former interior, foreign affairs and health minister.
Dlamini-Zuma pledged during her campaign to tackle the racial inequality that persists in South Africa since the end of white minority rule.
KwaZulu-Natal, which has the biggest delegation at the conference with 870, is the Dlamini-Zuma's stronghold. He also lashed out at the media, the judiciary and civil society, accusing them of fighting the ANC or interfering in party matters.
In August, Zuma narrowly survived another attempt in parliament to force him from office after some members of his party voted with the opposition in a no-confidence vote.