For the first time in 13 years, the opposition stands a chance of winning enough votes to force Morales into a second round. In elections in 2009 and 2014, Morales won by unprecedented margins of 61 percent and 64 percent respectively.
According to recent polling, the 59-year-old is still expected to receive the most votes, but it is unclear if he will capture the 40 percent needed and have a 10-point margin over the second-place finisher to avoid a runoff, which would be held on December 15.
A runoff would mean the fragmented opposition would have to work to overcome their differences and unite against him.
Morales’s closest rival is former President Carlos Mesa with the Citizen Community (CC) alliance, a coalition of opposition groups.
During the campaign, Mesa has focused on Morales’s failure to respect term limits.
Under Bolivia’s 2009 constitution, presidents can only serve two terms. Morales argued his first term was exempt from this rule because it took place before the new constitution.
In 2016, Morales’s Movement to Socialism party held a referendum to decide if he could run again. When he lost, he promised to respect the result. But, in late 2017, the country’s Supreme Election Tribunal ruled that preventing him from running would violate his human rights, prompting protests.
“We are here to defend democracy because it is at risk in our country,” Mesa said at his final campaign rally on Tuesday.
Right-wing Senator Oscar Ortiz, from the lowland city of Santa Cruz, Bolivia’s largest city, is polling in third place. His party, Bolivia Dice No (Bolivia says No), rejects the legitimacy of Morales’s candidacy and argues for cutting public expenditure.
He has been steadily losing ground to the campaign’s late arrival: Chi Hyung Chung, a far-right Korean-born, Christian evangelical who blames gender equality and homosexuality for the country’s problems.
Morales, the country’s first indigenous leader, was first elected on a leftist platform and as a champion for the poor and indigenous people.
Under his leadership, Bolivia has consistently had one of the region’s highest growth rates and has slashed poverty in half, according to the International Monetary Fund (IMF). The minimum wage has doubled and the national legislature has more indigenous people and women than ever before.
“We managed to increase the savings rate and that has translated into more consumption in the short term, and more investment in the medium and long term,” Finance Minister Luis Arce Catacora told Al Jazeera.
Many working-class Bolivians want these changes to continue.
“We don’t trust the opposition to continue what we’ve gained under Morales,” said Maria Quispe, a La Paz market vendor.
“That’s why Evo still has my vote,” she told Al Jazeera.
But Morales’s party has also shifted away from its early promises of societal transformation and moved towards the political centre.
Many Bolivians are angry at Morales’s decision to seek a fourth term and, more recently, his government’s slow response to recent forest fires. Many of his new social programmes and infrastructure have been funded by the expanded exploitation of Bolivia’s natural resources and an expansion of the agricultural frontier.
“If Evo wins, it won’t be a true democracy any more,” Steve Zambrana said at a Cochabamba demonstration protesting against Morales’s candidacy. “It will just be a sham.”
Polls will close at 4pm local time (20:00 GMT), and preliminary results are expected by early evening.