BUENOS AIRES (Reuters) - Argentina’s leftist ex-President Cristina Fernandez leads the candidate for President Mauricio Macri’s coalition in the Senate race for politically-crucial Buenos Aires province, a poll showed on Thursday.

Former Argentine President Cristina Fernandez de Kirchner waves during a rally in Buenos Aires, Argentina June 20, 2017. REUTERS/Marcos Brindicci

Fernandez, who as president spooked foreign investors but was popular with Argentina’s poor, got 32.2 percent of voter intention for Sunday’s primary vote ahead of October midterm legislative elections, according to the poll by Buenos Aires consultancy Management & Fit.

Sunday’s vote, in which no major candidate faces a challenger, is seen as a dry run for the final election and a referendum on fiscal austerity and market-friendly policies Macri put in place since taking office in 2015.

Former Education Minister Esteban Bullrich, the candidate for Macri’s ‘Let’s Change’ coalition, came in second in the poll with 28.1 percent.

While the race will not fundamentally change the balance of power in a divided Congress, a victory by Fernandez could pressure prices of Argentine assets on chances she might return to power in the 2019 presidential election.

Fernandez was known for interventionist policies and trade restrictions during her two terms in office from 2007 to 2015, as well as generous welfare spending.

A strong showing by Macri’s coalition in Sunday’s vote would reassure investors that his government will have the capacity to pass further reforms.

The peso currency has lost 9 percent of its value since Fernandez declared her candidacy on June 24. The central bank has sold more than $1 billion in reserves in the past two weeks to stop the currency’s slide, including a $298.2 million intervention on Thursday.

A third of Senate seats and half of lower-house seats are up for grabs in October’s election.

‘Let’s Change’ will likely triumph nationwide, Macri told Reuters in an interview as part of the Reuters Latin America Investment Summit this week. But races in Buenos Aires, with more than a third of Argentina’s electorate, are being closely watched for signs Fernandez allies could strengthen their hand in Congress and stall Macri’s reforms.

Sergio Massa, a relative moderate who came in third in the 2015 presidential elections, was third in the Senate poll at 23.1 percent.

Macri’s Buenos Aires candidate for the lower house fared better, gaining 29.1 percent of voting intention compared with 20.8 percent for Fernandez’s candidate.

The poll was conducted between August 7 and August 10 among 803 Buenos Aires voters. It had a 3.5 percent margin of error.