In a nationwide day of local polls whose results may worry the Kremlin, opposition anti-drugs campaigner Yevgeny Roizman also defeated the pro-Kremlin candidate in elections for Russia’s fourth-largest city Yekaterinburg.

Sobyanin, a long time ally of Putin, won 51.32 per cent of the vote and Navalny 27.27 per cent, the Moscow election commission said, in a count based on 99.6 per cent of polling stations reporting.

But Navalny, 37, insisted he had managed to force the mayor into a second round and vowed street protests if the authorities did not acknowledge Sobyanin had polled less than 50 per cent.

“What we are seeing now are clear falsifications,” he told reporters in a late night briefing at his campaign headquarters in Moscow.

“We demand that a second round is held. If that is not done ... we will appeal to the citizens and ask them to take to the streets of Moscow.”

The city authorities have already allowed Navalny to hold a rally of up to 2,500 people in central Moscow on Monday evening, during which he has promised to decide future strategy.

The candidacy of the charismatic anti-corruption crusader Navalny made the race the first genuinely competitive Russian election since the heady early post-Soviet years.

It was also the first time the Kremlin had allowed Muscovites to elect their mayor in a decade and Sobyanin clearly wanted to pick up popular legitimacy after being appointed in 2010 to replace longstanding mayor Yury Luzhkov.

In a late-night rally on Sunday in central Moscow attended by thousands and lit up by fireworks, Sobyanin said he was sure of victory and congratulated himself for organising “the most honest and open elections in the history of Moscow”.

“We have something to be proud of,” he told the cheering supporters with uncharacteristic passion.

Navalny’s camp expressed suspicion over the failure of the authorities to produce a final turnout figure but it was expected to be around 32 per cent.

Analysts said that the low turnout had helped Navalny, with the protest leader’s dynamic Western-style campaign doing a far better job of bringing out support than Sobyanin’s distinctly low-key push for votes.

Communist candidate Ivan Melnikov was third in the partial results with just over 10.6 per cent of the vote, while other contenders merely made up the numbers.

Moscow was shaken by huge demonstrations against Putin’s decade-long rule in the winter of 2011-last year and the elections gave Navalny a chance to revive the flagging momentum of the protest movement.

“This is a victory for Navalny, the results he’s received are very good, even if there will be no run-off,” Gleb Pavlovsky, a political analyst and one-time Kremlin consultant, said.

In the run-up to the vote, Navalny shook up Russian politics with a Western-style political campaign that made savvy use of the internet and secured more than 100 million rubles (HK$23.29 million) in donations.

By contrast, buttoned-up Kremlin functionary Sobyanin avoided overt political rhetoric and shunned television debates, instead focusing on sprucing up the parks and sidewalks in the capital of 12 million people.

In July, Navalny was sentenced to five years in a penal colony on fraud charges that he says were trumped up. He was jailed, but suddenly released a day later pending his appeal.

“The question is, what will they do to Navalny now,” said Nikolai Petrov, an analyst with the Higher School of Economics, saying he could be given a suspended sentence if the authorities feared protests.

In Yekaterinburg’s sole-round election, Roizman won 30.11 per cent of the vote while the candidate of the ruling United Russia Party, Yakov Silin, had 26.48 per cent, the local elections commission said.

It marked one of the first times in recent post-Soviet Russian history that an opposition candidate has beaten the ruling-party figure in a major city.