A bell tolled on TV, signaling a shift in the results tallied so far. From their home in northern Johannesburg, the Mathivha family celebrated the latest update: with the majority of votes counted, the African National Congress had earned a mere 41 percent.

“Good!” said Buhle Mathivha, pointing at the television screen.

“Good,” her husband, Khathu Mathivha, echoed.

“It should continue to decline, they are too arrogant,” Ms. Mathivha said.

The couple sat in front of a cozy fire on Friday evening in South Africa where it is almost winter, watching news coverage of what was to be a watershed election. For the first time since the end of apartheid in 1994, the party once led by Nelson Mandela failed to win an outright majority of the votes in a national election.

While the African National Congress, or A.N.C., remains the leading party in the May 29 election, the latest tally is widely viewed as a political defeat and a rebuke from voters like the Mathivhas who have become exasperated with the only party they have known since the end of apartheid. In the last election, in 2019, the A.N.C. took 57 percent of the vote. The drop to 41 percent in this election has cost the party its majority in Parliament, which elects the country’s president. Now, it will have to work with smaller opposition parties, like those the Mathivhas voted for instead of the A.N.C.

Buhle and Khathu Mathivha broke with family convention and their own previous votes when they decided not to vote for the A.N.C., a party they described as “pompous” and corrupt. Ms. Mathivha, 34, and Mr. Mathivha, 36, are part of the largest cohort of registered voters in South Africa. South Africans aged 30 to 39 make up nearly quarter of registered voters, and those slightly older, 40 to 49, make up more than a fifth.