Nayib Bukele. (Photo: CGTN)

Nayib Bukele declared victory in El Salvador's presidential elections on Sunday after securing a decisive lead over his two main rivals.

According to preliminary results from the Supreme Electoral Court (TSE), with more than 87 percent of ballots counted, the 37-year-old former mayor of San Salvador garnered a commanding 53.8 percent of the votes, enough to win the first round.

In a second place was Carlos Calleja, candidate of the conservative Nationalist Republican Alliance (ARENA), with 31 percent of the votes.

Hugo Martinez, candidate of the ruling leftist Farabundo Marti National Liberation Front (FMLN), trailed in third place, with nearly 14 percent of the votes.

"We have won in the first round, we made history," Bukele told supporters in a victory speech.

The FMLN's Martinez promptly conceded defeat, tweeting: "We are democrats and we respect institutions and respect the people's verdict. We recognize the results."

The president of the TSE, Julio Olivo, told the press "we have results that mark a definitive trend."

Bukele, the presidential candidate of the right-of-center Grand Alliance for National Unity, recently parted ways with the FMLN. His mayoral race was under the FMLN banner.

He went on to run a successful campaign as the anti-establishment alternative to the two main parties, namely the FMLN, which has governed the last two terms, and ARENA, which ruled for 20 years prior.

Bukele has pledged to fight corruption and break the domination of the two-party system.

More than 5.2 million Salvadorans were eligible to vote, including nearly 6,000 living abroad.