Sao Paulo, Brazil ? Former union boss Luiz Inacio Lula da Silva won Brazil’s presidential election runoff by a landslide Sunday, marking a historic shift to the left for Latin America’s largest country.

Ruling party candidate Jose Serra conceded defeat, shortly after Silva’s Workers Party had declared their candidate the winner.

“I think Brazil can play an extraordinary role in this American continent, so that we can build an effective world peace, where countries can grow economically and socially for the well-being of their people,” Silva said in his victory speech, as thousands of his supporters celebrated in the streets.

A somber Serra, a former health minister backed by the outgoing government, wished Silva “good luck in leading the destiny of Brazil” in a concession speech at his campaign headquarters.

With 99 percent of the vote counted, Silva a former shoeshine boy who rose to become the head of a labor union had 61 percent and government-backed candidate Jose Serra had 39 percent, the government Supreme Electoral Tribunal announced.

Thousands of Silva supporters gathered in the streets of Sao Paulo and Rio de Janeiro, waving his party’s red flag in celebration.

“This is our opportunity to consolidate our hopes for a Brazil which should be more just, and care more about the needs of the people,” said Marcos Xavier, a university professor who stood amid some 1,000 Silva supporters on Sao Paulo’s main avenue.

While the votes were still being counted, the White House offered its congratulations to the winner.

“The president congratulates the winner of the election and looks forward to working productively with Brazil,” said press secretary Ari Fleischer, speaking to reporters aboard Air Force One, while returning from an economic summit in Mexico.

Silva’s criticism of free-market policies is at odds with Washington. His election could complicate President Bush’s goal of creating a hemispheric free-trade zone by 2005. But the administration has been careful not to criticize Silva during the campaign, aware that any comment could be seen as interference.

Silva, popularly known as “Lula,” just missed a victory in the first-round election on Oct. 6, forcing a runoff against Serra, a former health minister with the ruling party.

Silva’s election marks a historic shift to the left for Brazil, which has never elected a leftist president. Its last leftist leader was Joao Goulart, a vice president who assumed power in 1961 when the centrist president resigned. Goulart served 2 1/2 years before being deposed by a right-wing military coup.