Flávio Bolsonaro, a senator and the son of former president Jair Bolsonaro, finished first in Brazil's presidential vote on Sunday with 47.03% against 45.16% for President Luiz Inácio Lula da Silva. Neither cleared 50%, so the two meet in a run-off on October 25.

President Milei, who backs Bolsonaro, congratulated his "dear friend" on election night for what he called a "historic election" against "the communist Lula." On Monday he posted that "a leftist communist loses to someone on the right and the markets celebrate with big gains," adding: "Leftist impoverishers, get out of the way, we are trying to make the continent shine."

For Argentina, the stakes run through trade. Brazil is Argentina's largest trading partner, and the car industry is the most exposed: it accounts for about 40% of trade between the two countries, according to Gustavo Pérego of the consultancy Abeceb, so Brazilian demand and the exchange rate matter more to Argentine factories than either candidate's politics.

A stronger real helps. It makes Argentine goods cheaper for Brazilian buyers and Brazilian goods dearer in Argentina. Leonardo Chialva of Delphos Investment said a stronger real takes pressure off Argentina and brings calm to the exchange rate, which he called the market's biggest fear in 2027, the year of Milei's re-election bid.

The Casa Rosada has a second goal. Milei wants to overhaul Mercosur, including a review of its common external tariff and more freedom for members to sign their own trade deals, and the government sees a Bolsonaro presidency as a window to push it. Pérego expects a Lula government to keep a distant relationship with Milei, with talks run mainly by technical teams. A Bolsonaro government could be more open to cutting trade barriers, which would expose Argentine auto-parts makers to more competition, he said.

Milei held a cabinet meeting at the Casa Rosada on Monday that also covered his legislative agenda, including a push to scrap Argentina's open primaries (PASO). Some ruling-party figures urged caution: one told Infobae the Brazilian result alone will not be enough to help Milei in 2027, because the run-off comes first.

Lula called the result "unexpected" and said he expects to win the run-off.