Russian protest leader Alexei Navalny on Sunday takes on a Kremlin-backed incumbent in a hotly contested Moscow mayoral poll, the first time the Kremlin has allowed a bitter opponent of President Vladimir Putin to stand in a high-profile election.
Muscovites will go to the polls to elect a mayor for the first time in a decade that has seen Putin scrap regional elections and then reinstate them after huge protests against his rule in winter 2011.
Navalny's participation created the first genuinely competitive choice in a Russian election in years, even if current Moscow mayor Sergei Sobyanin is expected to secure re-election in the first round.
Many observers see the poll in the city of 12 million as a vote of confidence in Putin's top-down power structure as disenchantment with the strongman's 13-year rule grows in the affluent capital and economic trouble looms ahead.
"Moscow mayoral elections are much more than just Moscow mayoral elections," said Lilia Shevtsova, a political analyst with the Carnegie Moscow Centre.
"The election should show us just how popular Putin is in Moscow, and therefore a mayoral election is turning into a key political factor."
The main intrigue in the upcoming polls is not how many vote for the pro-Kremlin incumbent but what happens to his main rival Navalny, who has been campaigning under the burden of a five-year prison sentence on what he says are trumped-up charges.
The blogger, who made a name for himself exposing corruption among the elites, has vowed to jail Putin and his allies if he is one day elected president.
At the start of the campaign, Navalny was sentenced to five years in a penal colony on fraud charges and arrested in court.
A day later he was suddenly released pending appeal of his term, in an unprecedented move observers say showed the Kremlin did not know how to handle Navalny.
Just days before the poll, Putin in a television interview rubbished Navalny's ability to be mayor and claimed that wherever the opposition leader goes, "some kind of problem follows".
Putin, who has hardly ever commented on the 37-year-old, appeared to go out of his way to avoid referring to Navalny by his name and instead described him as "this gentleman".
--- 'The hardest job of my life' ---
Navalny has run what many say is the first Western-style political campaign in Russia, holding countless meetings with everyday Muscovites and promising to cleanse the city of corruption.
He mobilised the support of thousands of volunteers and more than 100 million rubles ($3 million) in donations.
He secured the public backing of dozens of entrepreneurs and hired Sergei Guriyev, a prominent economist who fled Russia this year after pressure from the authorities, to write his economic programme.
A charismatic orator who roused crowds with his fiery speeches during unprecedented protests against Putin, Navalny admits he is a political neophyte and learnt the ropes of campaigning from American political television series like The Wire, House of Cards and Homeland.
"These three to four meetings with voters a day are the hardest job of my life," he told opposition weekly The New Times.
Sobyanin, a 55-year-old buttoned-up Kremlin functionary, runs a very different kind of campaign.
He has refused to participate in television debates and given few interviews, instead focusing his energies on sprucing up the capital ahead of the vote.
A trusted insider, he previously served as the Kremlin's chief of staff and the governor of the oil-rich Tyumen region. He was appointed to the current post in 2010 after then Moscow mayor Yury Luzhkov fell out with the authorities.
-- 'Winning in the capital of protests' ---
"Moscow is the capital of political protests," said Nikolai Petrov, an analyst at the Higher School of Economics.
"It's important for the Kremlin to show that even at the epicentre of the protests he will receive a majority of votes."
Sobyanin is set to win the polls with a majority in the first round, while Navalny is expected to come second with 18 percent, according to independent pollster Levada Centre.
Besides Sobyanin and Navalny, four other candidates are running in the polls but support for most of them is not significant.
Despite their differences, most candidates made toughening immigration policies a key plank of their campaigns, vowing to rid the city of tens of thousands of migrant workers from ex-Soviet Central Asia.
Navalny charges that authorities are planning to rig Sunday's elections, and many expect his supporters to take to the streets after the vote.
Analysts say Navalny's future depends on his performance in the poll and the scale of the protest after it.
"I do not rule out that his prison term could be commuted to a suspended sentence," said Dmitry Orlov, a political analyst who consults the presidential administration.
On Sunday, Russians will also elect local lawmakers and mayors in a number of cities including the Urals city of Yekaterinburg where an opposition activist is expected to run against a Kremlin-backed rival.