A court has found Deputy President Jacob Zuma's former financial adviser guilty of corruption and fraud, increasing pressure on the man who had been seen as the country's next leader.
The decision immediately revived opposition calls yesterday for President Thabo Mbeki to fire his deputy, and for parliament to reopen an inquiry into a multibillion-dollar arms deal at the centre of the case.
Judge Hilary Squires of the High Court in Durban found Schabir Shaik, a flamboyant businessman regarded as the ruling African National Congress (ANC)'s banker at the height of the anti-apartheid struggle, guilty of corruption and fraud for paying kickbacks and bribes to Mr Zuma in exchange for favours in the arms deal.
Shaik, a friend of Mr Zuma from the anti-apartheid struggle, had been accused of trying to solicit a bribe of 500,000 rand (£40,000) each year for Mr Zuma from a French arms firm called Thint, a subsidiary of Thales International (formerly known as Thomson-CSF), in return for protecting it from an investigation into an arms deal arranged by South Africa in the 1990s.
The other corruption count charged that Shaik had paid Mr Zuma 1.3m rand in bribes to induce Mr Zuma to use his political influence to further Shaik's business interests, while the fraud charge related to accounting for these payments.
Mr Zuma has denied corruption, and Shaik rejected the verdict.
President Mbeki is returning from Washington, where he was attempting to convince President George Bush to back Tony Blair's project of sending billions of dollars to eradicate poverty in Africa.
Mr Mbeki also visited other G8 leaders to allay their fears that the increased aid would end up being looted by corrupt African dictators. But he now faces his test case to lead by example and deal decisively with his deputy ahead of the G8 summit, at which he will be Africa's main representative.
Virtually all of South Africa's opposition parties, led by the official opposition Democratic Alliance (DA), called for Mr Zuma's resignation or firing yesterday, saying his case had severely tarnished the country's international image.
In fact, the DA's chief whip, Douglas Gibson, wasted no time moving a no confidence motion against Mr Zuma in the National Assembly. "I ... move that this House has no confidence in the Deputy President, and that he should resign forthwith. If he fails to do so, [the] President should dismiss him," he said.
Although Mr Zuma himself was not on trial, Judge Squires found that the Deputy President had maintained a "generally corrupt relationship" with Shaik.
Mr Zuma had earlier denied corruption, while Shaik said: "I walk in the light of my Lord. I'm innocent ... till I meet him.".
But analysts said the verdict may reopen the door to criminal charges against Mr Zuma after the former director of public prosecutions Bulelani Ngcuka had spared charging the Deputy President, even though he said there was a prima facie case against him.
That statement infuriated Mr Zuma's supporters, who said Mr Ngcuka was an apartheid-era spy. A commission of inquiry instituted by President Mbeki cleared Mr Ngcuka, but he later opted to resign.
There are now new demands to investigate whether or not Mr Ngcuka had been pressured not to prosecute Mr Zuma.
Analysts and opposition parties have also called for a reopening of investigations into the corruption- riddled arms deal following Shaik's conviction.
Mr Zuma said he was studying the judgment and would comment later.