KINSHASA (Reuters) - Democratic Republic of Congo’s electoral commission on Thursday declared opposition leader Felix Tshisekedi the surprise winner of last month’s chaotic presidential election, but the runner-up dismissed the outcome as an “electoral coup”.

The result sets the stage for Congo’s first democratic transfer of power, but also a tense political standoff with the potential for the kind of violence that followed polls in 2006 and 2011 whose outcome was contested.

Vote tallies by Congo’s Catholic church (CENCO) showed second-placed opposition candidate Martin Fayulu as victor, according to two diplomats briefed on the findings.

Tshisekedi won with 38.57 percent of more than 18 million ballots cast, Corneille Nangaa, the president of the election commission (CENI), told a news conference at 3 a.m. (0200 GMT) that seemed timed to avoid any immediate reaction in the streets.

“Felix Tshisekedi Tshilombo is declared the provisionally- elected president of Democratic Republic of Congo,” Nangaa said, to a mixture of cheers and gasps inside CENI headquarters.

In the Kinshasa neighborhood of Limete where Tshisekedi lives, thousands of people danced in the streets in celebration and cars slowed down and honked their horns.

Some chanted that Congo had “turned the page” on the Kabila era, which began in 1997 when Joseph Kabila’s father, Laurent, led a rebellion that overthrew longtime leader Mobutu Sese Seko. Joseph took over in 2001 when Laurent was assassinated.

“For a ruler to pass power to an opponent is rare, and it gives hope for the rest of Africa,” said John, a school teacher in Kinshasa who declined to give his full name.

“We now want change with this new power. Poverty, insecurity, killings, we must finish with all this.”

Speaking to cheering supporters at his campaign headquarters, Tshisekedi paid his respects to outgoing President Joseph Kabila, whom he called “an important political partner”, and promised to rule for all Congo’s 80 million people.

“I will not be the president of a political organization ... I will not be the president of a tribe ... I will be the president of all Congolese,” he said.

If Tshisekedi’s victory is confirmed in the next 10 days by the constitutional court, he will become the first leader to take power at the ballot box since Prime Minister Patrice Lumumba, who was toppled in a coup less than three months after independence in 1960 and killed four months later.

Opposition fears that authorities would rig the vote in favor of Kabila’s hand-picked candidate, Emmanuel Ramazani Shadary, did not materialize as Shadary finished a distant third to Tshisekedi and Fayulu, with about 4.4 million votes.

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However, the result will fuel suspicion among Fayulu’s supporters that Tshisekedi, shown by pre-election opinion polls to be running well behind Fayulu, struck a power-sharing pact with Kabila.

Tshisekedi’s camp has acknowledged contact with Kabila’s representatives since the vote but said they were aimed at ensuring a peaceful transition and denied there had been any deal.

In an interview with Radio France Internationale, Fayulu, who was backed by prominent foes of Kabila, described the vote as an “electoral coup”.

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“The results have nothing to do with the truth of the ballot box,” he told RFI, and called on observers of the Dec. 30 vote to publish the real results.

CONTESTATION

Tshisekedi is the son of the legendary Etienne Tshisekedi, who led opposition to three successive presidents over 35 years. Felix’s profile rose when his father died in 2017 after helping to negotiate Kabila’s reluctant departure.

Kabila initially refused to step down when his mandate ended in 2016. In an interview last month, he did not rule out running again for president in 2023.

Losing candidates can contest Tshisekedi’s victory before Congo’s constitutional court, which has 10 days to hear and rule on any challenges.

Any widespread perception the election has been stolen could set off a destabilizing cycle of unrest, particularly in the volatile eastern borderlands where Fayulu enjoyed some of his strongest support.

The Catholic Church’s bishops conference said last week that it knew the identity of the winner and demanded that CENI publish accurate results. The Church did not say who it thought the winner was, but briefed diplomats on its conclusions. CENCO was not immediately available for comment after the results.

The vote was initially delayed by a week in part because of a fire that destroyed ballot papers. Authorities canceled voting on election day for more than one million people, saying the vote could not go ahead because of an Ebola outbreak and militia violence.

Observers said many polling stations opened late and closed early and in some places voting machines malfunctioned.