JOHANNESBURG — South Africa’s long-ruling African National Congress was headed to another big victory in national elections on Thursday, though it appeared to fall short of President Jacob G. Zuma’s goal of a two-thirds majority, incomplete results showed.

The A.N.C. led with 63 percent of the vote after nearly 83 percent of the ballots had been tallied, in keeping with projections that the party, mired in corruption scandals and headed by the unpopular Mr. Zuma, would shed a few percentage points off its share of the total this election. In the last general election, in 2009, it won 65.9 percent of the vote.

If the A.N.C.’s lead holds until the final returns are tabulated on Friday, Mr. Zuma, who has battled charges of corruption and rape in recent years, should easily earn a second term.

Party officials, appearing on television throughout the day, seemed relieved. An overwhelming victory was never in doubt in what has effectively been a one-party state since the A.N.C., under Nelson Mandela, won South Africa’s first all-race election in 1994.