Iran was on the brink of an extraordinary political transformation on Saturday night after the moderate cleric Hassan Rouhani sensationally secured enough votes to succeed Mahmoud Ahmadinejad.
Rouhani's victory delighted reformers who have been desperate for a return to the forefront of politics after eight acrimonious years under Ahmadinejad.
It will also lift the spirit of a nation suffering from its worst financial crisis for at least two decades as a result of the sanctions imposed by western powers in the dispute over its nuclear programme.
Rouhani, who favours a policy of political openness, as well as re-establishing relations with the west, is likely to soothe international tension. He has been described by western officials as an "experienced diplomat and politician" and "fair to deal with".
Iran's interior minister, Mostafa Mohammad-Najjar, announced on state television on Saturday night that 72% of 50 million eligible Iranians had voted, and Rohani had won just over the 50% of the vote required to avoid a runoff.
Rouhani, a PhD graduate from Glasgow Caledonian University and a former nuclear negotiator, has pledged to find a way out of the current stalemate over Iran's nuclear programme, which is the cause of the sanctions crushing the economy.
Minutes after he was announced as the winner, thousands of jubilant campaigners and people across Iran poured into streets to celebrate. "Ahmadi Bye Bye", chanted a large group in central Tehran, according to witnesses, in a reference to Ahmadinejad. Car horns were honking in larger streets in Tehran and Rouhani supporters chanted.
The Iranian currency, the rial, recovered in value against the dollar by at least 6% on Saturday. Later on Saturday night, Rouhani issued a statement on television, saying "a new season of solidarity" had begun following a result that brought "rationality and moderation" as well as "peace, stability and hope".
The country's supreme leader, Ayatollah Ali Khamenei, along with Ahmadinejad, congratulated Rouhani. Tehran's mayor, Mohammad-Bagher Ghalibaf, also conceded defeat by sending a congratulatory message to the president-elect. Other candidates did the same.
During Rouhani's term as a nuclear negotiator, Iran appeared more co-operative to the international community and, leading up to Friday's poll, he repeatedly pointed out that on his watch Iran's nuclear dossier was not referred to the UN security council.
Britain on Saturday night urged Iran's new president to set his country on a "different course" after years of deadlock and dispute with the west. The Foreign Office said that it hoped Rouhani would use his victory to engage with international concerns over Iran's nuclear ambitions and develop a "constructive" relationship with the wider international community.
"We call on him to use the opportunity to set Iran on a different course for the future: addressing international concerns about Iran's nuclear programme, taking forward a constructive relationship with the international community, and improving the political and human rights situation for the people of Iran."
White House spokesman Jay Carney said: "It is our hope that the Iranian government will heed the will of the Iranian people and make responsible choices that create a better future for all Iranians."
Analysts believe rigging was less likely this year because Ahmadinejad was not running and the government had not endorsed any of the candidates.
The endorsement of Rouhani earlier in the week by reformist leaders Mohammad Khatami and Akbar Hashemi Rafsanjani injected last-minute excitement into the race, boosting his chances. The 65-year-old was the only cleric among the six presidential candidates.
Meir Javedanfar, an Iranian politics lecturer at the Inter-disciplinary Centre in Israel, described the results as a "total and absolute surprise. Based on the 2009 results, which many including myself believe were falsified, the expectation was that Rouhani's genuine votes would not be counted, as his views do not seem to be in line with Iran's Revolutionary Guard Corps and the supreme leader, just like [opposition leaders] Mir Hossein Mousavi and Mehdi Karoubi's views were not," he said.
The former British foreign secretary Jack Straw knows Rouhani and described him as "warm and engaging".
"This is a remarkable and welcome result so far and I'm keeping my fingers crossed that there will be no jiggery-pokery with the final result," he said.
"What this huge vote of confidence in Rouhani appears to show is a hunger by the Iranian people to break away from the arid and self-defeating approach of the past and for more constructive relations with the west." He added: "On a personal level I found him warm and engaging. He is a strong Iranian patriot and he was tough but fair to deal with and always on top of his brief."
Speaking to the Observer, Seyed Hossein Mousavian, Rouhani's deputy on Iran's national security council from 1997 to 2005, and a spokesman for Iran's nuclear negotiating team, said the results showed Iranians were desperate for change.
"The public support of Mr Rafsanjani and Mr Khatami and withdrawal of Mohammad-Reza Aref from the race had a major role in Rouhani's win," he said. Khatami and Rafsanjani played a significant role in Rouhani's victory by holding off declarations of support and persuading Aref to drop out to avoid a split vote.
"Hardliners remain in control of key aspects of Iran's political system, but centrists and reformists have proven that even when the cards are stacked against them they can still prevail due to their support among the population," Trita Parsi of the National Iranian American Council said.
The turnout for Friday's vote was so high that polling stations stayed open for five hours longer than planned.
Speaking after casting his vote in Tehran, Khamenei had urged a mass turnout to rebut suggestions by American officials that the election enjoyed little legitimacy.
"I recently heard that someone at the US national security council said, 'We do not accept this election in Iran'," he said. "We don't give a damn."
Among those voting was Ebrahim Yazdi, secretary general of the Freedom Movement of Iran, a banned group that is critical of the system.
"Today's election is about choosing between bad and worse," he told the semi-official Mehr news agency. "Voting is a national duty and a right given to you by God."
