By Elizaveta Gladun

BUCHAREST (Reuters) - Romania's European allies and markets welcomed centrist Nicusor Dan's presidential election victory over a eurosceptic hard-right rival on Sunday, relieved that the European Union member had avoided a lurch to a Donald Trump-inspired political path.

Dan, a softly-spoken 55-year-old mathematician and Bucharest mayor, won 54% of votes in the country of 19 million, beating George Simion, a vocal Trump admirer whose strong showing in the first round of voting this month had rattled allies and investors.

One of Dan's first official conversations on Monday was with NATO Secretary General Mark Rutte.

"I told him Romania will remain a firm ally in NATO," Dan said, adding defence investment was a focus. "At the same time, we are counting on NATO to guarantee Romania's security."

Dan also spoke to French President Emmanuel Macron and neighbouring Moldova's President Maia Sandu, who had called the election result "a step forward for democratic values and our shared European path."

Dan had pledged to fight corruption, maintain support for Ukraine - where Romania has played an important logistical role - and keep the country in the European mainstream.

In contrast, Simion, a 38-year-old nationalist, had been critical of EU leadership and opposed military aid to Ukraine. His strong position before Sunday's run-off caused the collapse of Romania's pro-Western coalition government.

On Monday, the leu gained more than 1.5% after shedding as much as 3% this month in the run up to the election and Romania's euro-denominated bonds rallied.

Dan, who must appoint a new prime minister, was due to meet Interim President Ilie Bolojan to discuss the transition and upcoming coalition talks, a political source said.

European Commission President Ursula von der Leyen was one of the first to congratulate Dan.

"The Romanian people have turned out massively to the polls," she said on X. "They have chosen the promise of an open, prosperous Romania in a strong Europe."

Echoing that, European Council President Antonio Costa called the result "a strong signal of Romanians' attachment to the European project."

EU ALLIES APPLAUD

After years of rising nationalist sentiment in Europe, the EU was increasingly uneasy about the prospect of a shift to the hard-right in Romania. Analysts had said victory for Simion would have risked isolating Romania abroad and destabilising NATO's eastern flank.

Donald Tusk, prime minister in Poland where centrist Warsaw Mayor Rafal Trzaskowski and nationalist Karol Nawrocki will face off in a presidential election on June 1, applauded the result, as did Macron and German Chancellor Friedrich Merz.

"Despite numerous attempts at manipulation, Romanians tonight chose democracy, the rule of law, and the European Union," Macron said on X, in Romanian.

The election took place nearly six months after the initial ballot was cancelled because of alleged Russian interference - denied by Moscow - in favour of far-right frontrunner Calin Georgescu, who was banned from standing again.

Russian-born Pavel Durov, the founder of the Telegram messaging app, on Monday accused the head of France's foreign intelligence agency of asking him to ban Romanian conservative voices ahead of the election, adding he refused the request. The intelligence agency denied the allegations.

Asked about Durov's comments, Kremlin spokesman Dmitry Peskov said that it was not news that European states such as France, Britain and Germany interfered in the affairs of other countries and said that the vote's conduct had been "strange, to say the least", state news agency TASS reported.

Analyst Radu Magdin said he expected Dan would pursue a common sense foreign policy.

"He will cultivate the Trump administration as much as possible while remaining a staunch European," Magdin said.

(Reporting by Elizaveta Gladun, Malgorzata Wojtunik, Krisztina Fenyo, Luiza Ilie; Editing by Jason Hovet, Alexandra Hudson)