Supporters of opposition presidential candidate Luis Lacalle Pou react at the party's headquarters as they wait for results after a runoff elections in Montevideo, Uruguay, Sunday, Nov. 24, 2019. Uruguayans are choosing between Presidential candidate for the ruling party Broad Front Daniel Martinez and Lacalle. (AP Photo/Santiago Mazzarovich)

MONTEVIDEO, Uruguay (AP) — The candidate of a united opposition held on to a razor-thin lead early Monday in Uruguay’s presidential runoff election, threatening to end a 15-year string of center-left governments, though officials said the count was too close to call a victor.

The National Party’s Luis Lacalle Pou, who lost a presidential runoff five years ago, led with 50.6% of the votes to 49.4% for the governing Broad Front coalition’s Daniel Martínez, with more than 99% of the ballots from Sunday’s election counted.

But in a closer than anticipated race to the finish, Lacalle Pou’s lead was just under 30,000 votes out of nearly 2.3 million tallied, forcing Uruguayans to wait to see if another electoral blow had been delivered to a left-leaning bloc in Latin America.

The Electoral Court said it could not yet declare a winner, given the closeness of the vote.

"There was never such a tight ballot," José Arocena, president of the Electoral Court, said early Monday. He said it would likely be Thursday before final, official returns can be announced.

Lacalle Pou predicted he would emerge as the victor, while Martínez declined to concede.

“The result is irreversible,” Lacalle Pou told a crowd of supporters who chanted, “President! President!”

Martínez earlier said that the vote was too close to call and that he would await the final results to be announced by electoral officials.

Lacalle Pou, a 46-year-old lawyer and a former senator, is anything but an outsider. His father is former President Luis Alberto Lacalle and his mother was a senator.

He criticized the administration of current President Tabaré Vázquez for a soft economy, reminding voters that the unemployment rate has risen to 9.2% and that more than 50,000 jobs have been lost in recent years. The center-right candidate also hammered at rising crime in the country of 3.4 million people and promised to rein in public spending to curb a rising deficit.

Martínez, a 62-year-old engineer who was recently mayor of Montevideo and previously industry minister, reminded voters of his party’s longer record, dating back to 2005. He says that when the Broad Front first came to power, 1 million people were living in poverty, almost one-third of the population. That number has plummeted to 8.1%.

Martínez, a member of the Socialist Party, represents the more moderate and center-left wing of the Broad Front, which is a coalition of social democrats, communists, Christian democrats and former guerrilla members.

Martinez is a noted cycling enthusiast while Lacalle Pou favors surfing.

Martínez earned the most votes in October’s first round, topping Lacalle Pou 39% to 29%. But the challenger managed to win the support of four parties that were knocked out by that balloting.

Uruguay so far has escaped the turbulent, sometimes partisan protests that have swept Chile, Bolivia and recently Colombia, and Vázquez took note of that as he voted Sunday.

“All Uruguayans have to feel proud of being the people we are, respectful of law, respectful of the constitution, respectful of the opposition,” he said.

Martínez also praised the calm. "This was a democratic party, of respect, of tolerance, where we were able to exchange greetings in the street with people who supported the other candidate," he said after the polls closed.

Vázquez seemed open to his own party’s possible loss: “I believe we have to alternate, people, parties. It’s always good to have a fresh mind, with another outlook, another will and another desire to do things.”

Vázquez led the Broad Front to power in 2005, ending dominance by the Colorado and National parties dating back to independence in 1828. The economy was healthy during his first term and that of his successor, José Mujica. But growth slowed in Vázquez’s second spell as leader, crime rose, an education reform flopped and Vice President Raúl Sendic was forced to resign in 2017 over corruption allegations.

Vázquez, a 79-year-old oncologist, announced in August that he had been diagnosed with cancer. His successor’s five-year term starts March 1.

Supporters of Presidential candidate for the ruling party Broad Front Daniel Martinez react at the headquarters in Montevideo, Uruguay, Sunday, Nov. 24, 2019. Uruguayans voted Sunday in a run off presidential election between Martinez and Luis Lacalle, from the opposition National Party. With the runoff election to close to call neither candidate is conceding to the other. (AP Photo/Matilde Campodonico)
Opposition presidential candidate Luis Lacalle Pou makes a thumb up after a runoff elections in Montevideo, Uruguay, Sunday, Nov. 24, 2019. Uruguayans are choosing between Presidential candidate for the ruling party Broad Front Daniel Martinez and Lacalle. (AP Photo/Santiago Mazzarovich)
Presidential candidate for the ruling party Broad Front Daniel Martinez, right, and Graciela Villar, his running mate, wave to supporters at their headquarters in Montevideo, Uruguay, Sunday, Nov. 24, 2019. Uruguayans voted Sunday in a run off presidential election between Martinez and Luis Lacalle, from the the opposition National Party. With the runoff election to close to call neither candidate is conceding to the other. (AP Photo/Matilde Campodonico)
This combination of file photos shows presidential candidate of the Broad Front ruling party Daniel Martinez, left, on Oct. 20, 2019, and rival Luis Lacalle Pou, leader of the opposition National Party, on Oct. 22, 2019, both in Montevideo, Uruguay. Lacalle Pou, who lost the presidential runoff five years ago, held a noticeable though apparently single-digit lead over the Broad Front’s Daniel Martínez in polls heading into the vote on sunday, Nov. 24, 2019. (AP File Photos/Matilde Campodonico)
Broad Front party supporters look dejected as they listen to the elections results in Montevideo, Uruguay, Sunday, Nov. 24, 2019. Uruguayans are choosing between Daniel Martinez of the Broad Front, and opposition candidate for the National Party Luis Lacalle, in today's runoff election. (AP Photo/Matilde Campodonico)
Supporters of opposition presidential candidate Luis Lacalle Pou wait for the election results at the party's headquarters in Montevideo, Uruguay, Sunday, Nov. 24, 2019. Uruguayans are choosing between Presidential candidate for the ruling party Broad Front Daniel Martinez and Lacalle. (AP Photo/Santiago Mazzarovich)