Opposition leader Alexei Navalny swept up far more votes than expected Sunday while finishing second in Moscow's mayoral election, a pivotal contest that has energized Russia's small opposition in ways that could pose a risk to the Kremlin in the days and years ahead.

Partial results released early Monday showed Navalny with about 27 percent of the vote, while the Kremlin-backed incumbent, Sergei Sobyanin, held a clear lead with about 52 percent. Exit polls, however, predicted Navalny would get as much as 32 percent.

As the results only began to trickle out two hours after the polls closed, Navalny said he suspected the vote count was being manipulated.

``We don't recognize the results that are currently being announced, and I would like to say that we won't give up one vote that we received,'' Navalny told reporters at his campaign headquarters late Sunday. ``I call on the Kremlin and the mayor's office to restrain themselves from falsifications.''

The election was being watched for what it bodes for the future of the opposition and for Navalny. He faces time in prison after being convicted of embezzlement in a case seen as part of a Kremlin effort to sideline him, but his strong showing could lead to a shortening of his five-year sentence, if the Kremlin feels this would help defuse discontent.

Sobyanin needs more than 50 percent to avoid a runoff, but if he is seen as squeaking through unfairly because of vote-rigging, it could set off protests. It was reports of widespread fraud in a national parliamentary election in 2011 that triggered the unprecedented demonstrations against President Vladimir Putin's rule.

Navalny's campaign said its own exit polls showed Sobyanin below 50 percent.

With ballots from about 70 percent of precincts counted, the results for Sobyanin and Navalny were holding steady at about 52 percent and 27 percent, respectively. The four other candidates trailed far behind.

Golos, Russia's leading independent election monitor, said the voting appeared to have gone smoothly, but there were fears that election officials would artificially increase the turnout to allow them to add votes for Sobyanin.

``This is the dilemma: Either they manipulate something somehow, but then they could be caught and won't be able to sleep soundly on Monday,'' Golos co-chairman Grigory Melkonyants said. ``Or they could let it be a real election and allow a second round.''

Unusually, election officials had not released a final turnout figure by early Monday. Two hours before the polls closed, turnout was registered at a low 26.5 percent. 

Navalny's campaign manager, Leonid Volkov, said Navalny would wait to make a statement on the election until the turnout was announced.

Golos observers noted that voter rolls at some polling stations had been padded with people who no longer lived in the neighborhood. They also noted that many people coming to the polls who receive benefits or salaries from the state had been pressured to do so. One woman demanded a document stating that she had voted, supposedly as proof for the state hospital where she worked, the group said.

Anna Grishina, a retiree who came out of the polling station soon after Navalny, clutched her cane and said proudly that she'd voted for Sobyanin.

``I don't see them,'' she said, when asked about which changes Sobyanin had brought to the city. ``But I hear about them on TV. He's opened new metro stations and redone the roads. I can't remember all of the things right now.''

The elderly are Sobyanin's core constituency, while the young and middle class are more likely to oppose Putin and his team. Sobyanin was Putin's deputy from 2005 until he was appointed Moscow mayor in 2010.

``Sobyanin and Putin spend most of their time lining their own pockets,'' said Alexei Gorshkov, a 34-year-old employee in the IT sector who voted for Navalny. ``It doesn't matter who you vote for today, as long as you vote against Sobyanin. If there's a run-off, Navalny will have a real chance.''

Navalny first built his following online through his anti-corruption blog, but it was the protests of 2011 and 2012 that cemented his status as de facto leader of the opposition. He led street marches that attracted tens of thousands of people from across the political spectrum.

His mayoral candidacy inspired a grassroots campaign like nothing the city had ever seen before. About 20,000 volunteers hit the campaign trail for Navalny, passing out leaflets in the metro or hanging banners on balconies. Navalny held impromptu campaign rallies outside subway stations several times a day.

Sobyanin did not actively campaign, preferring instead to play the regal incumbent and let his work as mayor speak for itself.

Sunday's mayoral election was the first since 2003 and the first since the Kremlin last year reversed Putin's 2004 decree abolishing direct elections for the Moscow mayor and other regional leaders.

Since Putin returned to the presidency for a third term, the Kremlin has cracked down on the opposition and tried to stifle dissent.

Navalny was sentenced in July to five years in prison for embezzlement in a case that he and his supporters describe as legally dubious and punishment for his exposure of high-level corruption. He left the courtroom in handcuffs, but a day later in a surprise turnaround, prosecutors requested he be set free until his appeal could be heard.

Most have speculated that it was Sobyanin who had Navalny set free, in order to ensure that the election would look as fair as possible and legitimize the Kremlin candidate as a politician. (AP)