The auction followed a five-year battle to force the government to pay legal costs, after it lost a court challenge against its controversial land reforms.
The farmers’ lawyer said it was a “symbolic victory” and vowed to target other Zimbabwe-owned properties.
Zimbabwe launched several court bids in a failed attempt to contest the ruling.
Property speculator Arthur Tsimatakopoulos bought the house for about $282,000, reports the BBC’s Mohammed Allie in Cape Town.
But most of the cash will go on legal costs, the farmers’ lawyer Willie Spies said.
“This is a symbolic victory and we will pursue other commercial properties owned by Zimbabwe,” said Mr Spies, who represented the farmers through AfriForum, a mainly white civil rights group in South Africa.