Conservative opposition candidate Mauricio Macri stunned Argentina's ruling party with an unexpectedly strong showing in the presidential election on Sunday, forcing a runoff vote next month, preliminary results showed.
Daniel Scioli, backed by outgoing leftist president Cristina Fernandez and her Front for Victory party, had a big lead in pre-election opinion polls and he had hoped for an outright victory on Sunday.
But the results showed the two men running neck-and-neck. With returns in from 86 percent of polling stations,Scioli had 35.9 percent support while Macri had 35.2 percent.
"What happened today will change politics in this country," Macri, the pro-business mayor of Buenos Aires, said in a speech to supporters.
The outcome of the election will shape how the South American country tackles its economic woes, including high inflation, a central bank running precariously low on dollars and a sovereign debt default.
Scioli could extend his slight lead as the remaining votes come in but the two men are now certain to go to a runoff election on Nov. 22 and Scioli looks vulnerable.
"Now the real election begins!" exclaimed Maria Astigarraga, a 45-year-old doctor, inside the music-filled campaign headquarters of Macri's 'Let's Change' alliance.
To avoid a second round of voting, either candidate would have needed 45 percent support on Sunday, or 40 percent with a 10 percentage point lead over his closest rival.
The results were met by deathly silence at Scioli headquarters, where minutes before supporters had been celebrating what was expected to be a convincing lead or even outright victory by governor of Buenos Aires province.
"I'm not surprised that the margin is narrow but I never imagined Macri would be on top," said one stunned Scioli supporter when earlier returns showed Macri ahead.
"The polls were totally wrong. This is totally unexpected," said political analyst Ignacio Labaqui. "An eventual Scioli victory, which was the consensus forecast, is clearly at stake."
In a speech before thousands of party militants, Scioli earlier reached out to swing voters for their support.
"United together we will triumph," Scioli told voters in a rallying call. "I call upon the undecided and independent voters to join this cause."
Still, some supporters worried that he would now lose the election.
"I'd like to tell you we can turn this around in November, but I don't know," said one who identified herself as Sandra at campaign headquarters.
Scioli, a former powerboat champion, draws much of his support from poorer Argentines who credit Fernandez and her late husband and predecessor Nestor Kirchner with an expansive welfare system and lifting the economy out of a 2001-2002 economic depression.
Fernandez was constitutionally barred from seeking a third consecutive term this year, but she could return as a presidential candidate in 2019.
Macri has vowed to start dismantling her protectionist currency and trade controls on his first day in office if he wins. Fernandez will hand over power to her successor on Dec.10.
In another damaging blow to the ruling party, Macri's alliance won the gubernatorial election in Buenos Aires province, Argentina's most populous, where Fernandez had hoped to install her cabinet chief Anibal Fernandez.