The liberal, pro-EU mayor of Bucharest, Nicusor Dan, has fought off a strong challenge from a Romanian right-wing nationalist to win the presidency after months of political turbulence.

George Simion, the leader of the far-right AUR party, won a dramatic first-round victory earlier this month, riding a wave of anger from Romanians who had seen the presidential race annulled late last year because of claims of Russian interference.

But it was the softly spoken Nicusor Dan who swept to victory, winning 54% of the vote in Romania, even though Simion was more successful in the diaspora.

“We need to build Romania together irrespective of who you voted for,” said Dan, once his victory was secure.

More than 11.6 million Romanians voted in Sunday’s run-off, and Dan attracted the support of more than six million of them.

The mathematician waited until after midnight on Sunday before he could be absolutely sure that the numbers were on his side and he could join his supporters in a park opposite City Hall in Bucharest.

They went wild, chanting his name and cheering. At one point he was almost mobbed but this was a huge moment for the president-elect and for his supporters after months of political tension.

“A community of Romanians who want a profound change in Romania won,” Dan said.

Mihai, one of many Dan supporters who gathered outside his electoral headquarters in the capital, told the BBC he was “really worried about Simion”.

“I want to choose the pro-European way. It’s the only way. It’s really important,” he added.

Andrea, who came with her young daughter, told the BBC: “We are so happy, we wanted to be here with other supporters of Nicosur.

“This means a better future for our children, for us. A good life for all of us, and an honest Romania.”

Romanians are broadly unhappy with the dominance of mainstream parties and the turbulence in this European Union and Nato member state intensified earlier this month when the government collapsed because its candidate had failed to make the second round.

While Nicusor Dan campaigned on fighting corruption and maintaining support for north-eastern neighbour Ukraine, Simion attacked the EU and called for cutting aid to Kyiv.

“Russia, don’t forget, Romania isn’t yours,” Dan’s supporters chanted.

Even though exit polls had given him victory, they did not include the all-important diaspora vote and Simion clung to the belief that he could still win.

“I won, I am the new president of Romania and I am giving back power to the Romanians,” he insisted initially.

It was not until the early hours of Monday that he conceded victory on Facebook. A protest planned by his supporters was then apparently called off.

During the election campaign Simion had stood side by side with Calin Georgescu, the far-right fringe figure who had stunned Romania with a first-round presidential victory at the end of last year, buoyed by an enormous TikTok campaign.

The vote was annulled over allegations of campaign fraud and Russian interference and Georgescu was barred from running again. Russia denied any involvement.

Asked by the BBC on Sunday whether he was acting as Georgescu’s puppet, George Simion said: “The puppets are those who annulled the elections… I am a man of my people and my people voted for Calin Georgescu.

“Do we like democracy only when the good guy has won? I don’t think this is an option.”

He said he was a patriot and accused what he called the mainstream media of smearing him as a pro-Russian or fascist.

The key to Simion’s success in the first round was his extraordinary win among diaspora voters in Western Europe, including in the UK.

His supporters turned out in force again on Sunday, with partial results giving him 68.5% support in Spain, 66.8% in Italy and 67% in Germany. He also had the edge in the UK, where voters said they would have picked Calin Georgescu if authorities had not barred him from running.

“We didn’t know anything about [Georgescu] but then I listened to what he was saying, and you can tell he’s a good Christian,” said 37-year-old Catalina Grancea.

She had vowed to go back to Romania if Simion had won and her mother Maria said she too had voted for change: “Our children were forced to leave Romania because they couldn’t find any jobs there.”

However, Nicusor Dan’s voters came out in even bigger numbers both in Romania and abroad. In neighbouring Moldova 87% of Romanians backed the mayor of Bucharest.

The presidents of both Moldova and Ukraine congratulated him on his victory.

“Moldova and Romania stand together, supporting one another and working side by side for a peaceful, democratic, and European future for all our citizens,” said Maia Sandu.

“For Ukraine, as a neighbour and friend, it is important to have Romania as a reliable partner,” said Volodymyr Zelensky in Kyiv.

European Commission President Ursula von der Leyen said on social media that Romanians had turned out in massive numbers and had “chosen the promise of an open, prosperous Romania in a strong Europe”.

In the end this was an emphatic “No” vote to a staunch nationalist with an isolationist vision for Romania, a known provocateur and a man whose commitment to EU membership and to the bloc’s core values was not clear.

Despite his strong showing in round one, those Romanians who worried about what he stood for appear to have rallied to block him from power.

But Simion did win a significant chunk of the vote, and his message will still resonate with many.