BUENOS AIRES, Argentina (AP) — Argentines are entering the tightest presidential race since the return of the country's democracy, with conservative President Mauricio Macri facing an opposition ticket including ex-President Cristina Fernández.

Sunday's primary elections are expected to provide a strong hint of who might win October's vote.

That's because primaries are held simultaneously and voting is obligatory, making them a sort of early poll involving the entire electorate.

Markets could go up or down depending on whether business-friendly President Mauricio Macri or center-left ticket of Alberto Fernández and Cristina Fernández poll favorably.