Chileans are voting in a presidential run off between conservative former President Sebastian Pinera and centre-left candidate Alejandro Guillier, a senator and popular TV journalist.
Polls opened on Sunday at 11:00 GMT and will close at 21:00 GMT. Final results are expected on Sunday night.
Education reform, growing inequality and a stagnant economy are the key issues for voters but many are expected to stay home after a poor turnout in the first round of voting last month.
Billionaire businessman Pinera, who led the country from 2010 to 2014, had been widely predicted to win, but a strong performance in the first round by outsider candidates plunged the race into uncertainty.
The November 19 vote returned a lower-than-expected 36.6 percent for Pinera, while Guillier came second with nearly 23 percent.
A candidate needs 50 percent to win outright.
The main shock from the first round was the Frente Amplio (Broad Front) coalition, headed by journalist Beatriz Sanchez, which took 20 percent of the vote, more than double pollsters’ predictions.
Far-right candidate Jose Antonio Kast also exceeded expectations, gaining eight percent, and becoming a key ally for Pinera in the second round as a result.
Polling is banned in the weeks running up to the election but analysts say the results will depend on which candidate can best draw Chile‘s disenchanted electorate towards the centre.
“At the moment the race is completely open,” said Roland Benedikter, a political analyst.
“People are thinking ‘if Pinera comes to power, maybe the rich will thrive and there will be more employment, but if the left stays in power, with Guillier, then probably there will be more equality.’ There’s a mood in the air that it could go either way,” Benedikter told Al Jazeera.
Pinera and Guillier are battling to replace incumbent socialist President Michelle Bachelet, Chile’s first female president, who leaves behind a chequered legacy.
Bachelet ended her first term in 2010 with an approval rating of 84 percent, the highest since the country returned to democracy in 1989 following the dictatorship of General Augusto Pinochet. She won the presidency again four years later and will leave office in March of next year.
Bachelet struggled to implement ambitious reforms in her second term which, combined with a slew of corruption scandals, have left voters feeling uninspired.
“How could we not be dissatisfied?,” said Luis Briones, an English teacher from Temuco, a city in southern Chile.
“We don’t have enough money to save for a decent pension, pay for our children’s education, health insurance, or to buy a house. We have to choose among those or live in debt,” he told Al Jazeera.
More than half of Chile’s eligible voters, some 6.5 million people, did not participate in the election’s first round. Turnout has been low since mandatory voting was scrapped in 2012.
According to Benedikter, whether Pinera or Guillier come out on top on Sunday depends on who can best persuade voters who chose far-right and far-left candidates in the first round.
“Mobilisation of the voters is important for both candidates and that will be the decisive factor in this election,” he told Al Jazeera.
“There is a new ideological polarisation in Chile but because all elections in Chile are won in the centre, every representative of the right and the left must strive not to go too far towards the wings of their party,” he said.
This new polarisation was evident in the results from the first round.
In addition to Sanchez claiming third place, Broad Front also secured 20 seats in the lower house of Congress and its first seat in the Senate in congressional elections that took place on the same day as the presidential vote, ensuring its effect will be felt long after these elections.
“I think they will be the new political force in Chile, a third power” statistician and pollster Miguel Zlosilo told Al Jazeera.
“They will not disappear at the next election. I think it’s the opposite, they will be stronger,” he said.
While the party has not officially endorsed either candidate, key figures including Sanchez and former student leader Giorgio Jackson have backed Guillier, who will be hoping their support will convince Broad Front supporters.
Chile’s next president will face an altered political landscape both at home and abroad as the country figures out its own political identity amid a wave of regional elections.
According to Peter DeShazo, a professor of Latin American studies at Dartmouth College and former US diplomat, Chile is in a state of transformation.
“The political system is transitioning from the very stable old order of the centre left and centre right coalition to something new and it remains to be seen what that new political order is going to look like,” he told Al Jazeera.
“With more access to information, voting bases in all countries are looking deeper into the candidates and demanding more,” he said.
With six more presidential elections following in 2019, Chile’s neighbours will be awaiting Sunday’s results with interest.