SANTIAGO (Reuters) - Chile’s presidential hopefuls ended their campaigns in downtown Santiago on Thursday ahead of an uncertain runoff election whose outcome will determine whether the world’s top copper producer turns to the right or maintains its center-left track.

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Voters on Sunday will choose between billionaire conservative Sebastian Pinera and center-left senator and journalist Alejandro Guillier. During the November first-round election, a surprise surge by harder leftists confounded pollsters, sent markets plummeting and set the stage for a tighter-than-expected runoff.

“Everything points to a narrow margin of victory,” said Guillermo Holzmann, a professor at the University of Valparaiso. “It’s an unusual race in that it’s been difficult to gauge the electorate.”

Both Pinera and Guillier would keep in place the longstanding free-market economic model in Latin America’s most developed country. But candidates with more extreme views on both the right and left performed better than expected in November, leading both men to make concessions to try to win over voters whose first-round choice dropped out.

Uruguay former president Jose “Pepe” Mujica, a leftist icon in a Latin America that has largely turned to the political right, turned out to support Guillier.

“The conservative right has no future in Chile,” Guillier told his fans.

Pinera, 68, a former president and the market favorite, placed first with 36.6 percent of the vote in the first round. He has vowed to boost growth by cutting the corporate tax rate and scaling back outgoing President Michelle Bachelet’s tax, labor and education reforms that Guillier has vowed to deepen.

At Santiago’s Caupolicán theater, he promised “a new and better treatment of the middle class, older adults and children.”

The bearded Guillier, 64, from northern Chile, garnered 22.7 percent of the vote in November from backers hoping to preserve gains made in Bachelet’s government for students, women and workers, measures such as lower university fees and laws empowering unions.

Guillier has courted leftists by proposing to overhaul the country’s privatized pension system and rewrite the constitution. Pinera has sought to appeal to centrist voters by calling for free technical education for the poor and a public pension option.

Guillier narrowly edged out third place finisher Beatriz Sanchez of the leftist Frente Amplio. She received support from 20 percent of voters with promises to tax the “super-rich” to boost social spending and fight inequality.

Sanchez’s 1.3 million voters are seen as pivotal in the upcoming election. Voting is voluntary in Chile, and abstention has run high in recent years.

“It comes down to how many people stay home, and particularly, how many people stay home on Guillier’s side,” said University of Chile professor Robert Funk.