Ukrainians on Sunday were choosing between two sworn rivals in a bitterly-contested presidential election after a divisive campaign that sparked warnings of a repeat of the 2004 Orange Revolution protests.
The dour pro-Russia opposition leader Viktor Yanukovich has the edge on his more charismatic challenger, the pragmatic Prime Minister Yulia Tymoshenko after winning January's first-round poll in the ex-Soviet state of 46 million.
But the outcome of the run-off remains uncertain as opinion polls have been banned since the first round and Tymoshenko will be hoping to capitalise on her opponent's clumsy verbal gaffes in the campaign.
Amid a charged atmosphere, both have exchanged accusations of seeking to rig the vote and analysts warn the losing side is likely to take grievances to the courts or even the streets if the margin of victory is narrow.
In 2004, tens of thousands of people protested against election results that had initially handed victory to Yanukovich, unleashing the Orange Revolution that swept pro-Western President Viktor Yushchenko to power.
"A new revolution is highly unlikely but we have to await confrontations in the court, in parliament and in the street," said Volodymyr Fesenko, director of the Penta centre for political studies in Kiev.
In a sign of preparations for post-election protests, around 40 empty tents have appeared outside the building of the Central Elections Commission, an AFP correspondent witnessed.
Polls opened at 0600 GMT and are to close 12 hours later, when a clutch of exit polls are expected to give an immediate indication of the voting trend.
"I have always voted for Yanukovich. The Orange team were in power but did nothing," said Yuri, 30, a businessman as he cast his vote amid sub-zero temperatures but bright sunshine in Kiev.
But Elena Poliakova, 60 slammed him as a puppet of Ukraine's powerful oligarchs. "He cannot speak, he only knows how to read out what is written down for him."
Tymoshenko will be hoping her telegenic style will win over hesitant voters after branding Yanukovich a "coward" for failing to show up at a televised debate that left the prime minister debating against an empty lectern.
The last days of Yanukovich's campaign were also marked by some colourful gaffes which saw him insist the Russian playwright Chekhov was Ukrainian and confuse gene pool with genocide.
But with Ukraine hit worse by the global economic crisis than any other major European economy and GDP shrinking 15 percent in 2009, voters may have other concerns than the candidates' rhetorical skills.
Yushchenko was bundled out in the first round in a humiliating fifth-place finish, paying the price for the failure of the Orange Revolution to realise the country's dreams of stability and prosperity.
There are few glaring differences in the programmes of the two candidates and both are seen as palatable to Russia, which found Yushchenko's pro-Western slant indigestible.
Yanukovich has made a remarkable political comeback since the debacle of 2004, trying to shake off his image as a Kremlin stooge with the help of US political consultants.
While Yanukovich is often described as pro-Kremlin, Tymoshenko is seen as a champion of Ukraine's bid for EU integration. But recently she has made much of her close relationship with her Russian counterpart Vladimir Putin.
Yanukovich's critics fault him for never explaining the vote-rigging that courts said his camp committed in 2004 and point to two convictions for theft and assault in Soviet times that were erased in the 1970s.
To the prime minister's enemies, Tymoshenko is an opportunist happy to bend with every change in the political wind in her pursuit of power.
She was briefly held in prison on forgery and gas smuggling charges in 2001, while her rarely seen businessman husband Olexander was implicated in the same scandal and spent one year in jail and then two more years in hiding.
A decisive factor could be how many votes Yanukovich and Tymoshenko snare outside their traditional strongholds. Yanukovich has extensive support in the Russian-speaking east while Tymoshenko is popular in the nationalist west.
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