The comprehensive victory by Mr. Fernández and Mrs. Kirchner, members of Argentina’s Peronist political faction, “paves the way for the return to left-wing populism that many investors fear,” the consulting firm Capital Economics said in a note to clients.

“With a renewed focus on sovereign default risks, bonds, equities and the peso will come under severe pressure in the coming days,” the firm said in its note. “That said, falls in the currency might be tempered by intervention in the foreign exchange market.”

Argentina’s central bank intervened hours after local markets opened, selling $50 million in the foreign exchange market to defend the peso in the face of the huge sell-off. In the auction, the bank used its own reserves for the first time since last September, traders said. The bank later said it planned to sell another $50 million of reserves.

[Read more about the election result that surprised investors in Argentina.]

The peso’s collapse is unlikely to affect other markets, said Win Thin, who leads currency strategy at Brown Brothers Harriman in New York.

“It’s a very small market,” he said. “Ever since Macri reopened the markets, took some market-friendly measures, there’s been a trickle of activity back in the peso and Argentine assets in general. Money has been trickling back in but it is still very minimal.”