The Ukrainian presidential election, plagued by bitter controversy and scandals, is seen as an east-west showdown.
By Leonid Ragozin
Russia has shown strong support for Yanukovych (right)
Prime Minister Viktor Yanukovych and opposition leader Viktor Yushchenko represent two contrasting visions for Ukraine's future: one keeping the country in the realm of Russia's influence and another pushing towards integration with the EU and Nato.
While Mr Yanukovych draws support from Russian-speaking eastern Ukraine, Mr Yushchenko represents the Ukrainian-speaking western regions.
The outcome will determine not only Ukraine's direction for the next decade, but will also influence the course of the entire former USSR.
Mr Yushchenko won the 31 October first round by an extremely narrow margin amid accusations of widespread fraud in favour of Mr Yanukovych, who is supported by the incumbent president, Leonid Kuchma, as well as Moscow.
Mr Yushchenko's headquarters and some observers say his lead was really much greater and that the vote-count was deliberately delayed by the authorities.
Moscow made it clear that it was fully behind Mr Yanukovych. Russia's most successful spin doctor, Gleb Pavlovsky, who was instrumental in turning Vladimir Putin into Russia's most popular politician, is now said to be playing the key role in Mr Yanukovych's campaign.
The streets of Moscow are full of huge billboards showing Mr Yanukovych, who hopes to collect the votes of numerous Ukrainians now living in an economically healthier Russia.
On the eve of the first round, President Vladimir Putin visited Kiev - officially to celebrate the anniversary of Ukraine's liberation in World War II. Footage of Mr Putin and Mr Yanukovych standing together during the celebrations was shown widely on Ukrainian and Russian television.
Mr Putin also starred in an unprecedented interactive TV show, answering dozens of phone calls from Ukrainian viewers.
After it became apparent that Mr Yanukovych had lost the first round, Mr Putin rushed back to Ukraine to wish Mr Yanukovych "good luck" in front of the cameras.
Meanwhile, Ukrainian media coverage of the campaign - widely criticised as biased in favour of Mr Yanukovych - underwent what was dubbed a "journalists' rebellion" between the two rounds.
A statement signed by 41 journalists from Ukraine's five main TV channels - including the state-owned ones - said Ukrainian TV had "kept quiet about major developments or distorted their essence under pressure from the owners and management".
Which of the Viktors will be the victor?
The journalists demanded "responsible coverage" in the run-up to the second round.
After an initial refusal Mr Yanukovych agreed to take part in face-to-face TV debates with Mr Yushchenko, whose face still bears terrible marks from alleged poisoning.
Ahead of Sunday's run-off vote the candidates were battling to woo the supporters of three left-wing candidates who came in behind them in the first round.
Left-wing voters are concentrated in the eastern Russian-speaking regions, where people are most fearful of the disruption of economic ties and travel between Ukraine and Russia.
Mr Yushchenko's cause was not helped by a group of leading Ukrainian writers who, declaring their support for the opposition, called the Russian language "a tongue of bandits".
In contrast, Mr Yanukovych has pledged to increase the status of the Russian language.
Key integration role
Why has Russia put so much effort into ensuring Mr Yanukovych wins in Ukraine?
"Ukraine plays a key role in any integration project in the former Soviet Union," says Kiev-based analyst Oleksander Lytvynenko.
"The loss of Ukraine as a participant in integration processes would have a grave political and psychological impact on Russia," he says.
Because of the shared medieval history of the eastern Slavs, Ukraine is still seen in Moscow as the cradle of Russian statehood - a key component of the pre-1917 Russian empire.
And in 1991 it was Ukraine's reluctance to participate that persuaded the new post-Soviet authorities in Moscow to abandon the idea of setting up a new union.
Now President Putin is trying to restore Russia's influence in the former Soviet Union through the Joint Economic Space Treaty signed by Belarus, Kazakhstan, Russia and Ukraine.
The treaty envisages that national governments will delegate some of their authority to a body similar to the European Commission. Mr Yanukovych fully supports the plan, but Mr Yushchenko's supporters believe it would spell a loss of sovereignty.
Western officials meanwhile have voiced cautious but clear support for Mr Yushchenko, seen as a person capable of raising standards in Ukraine's political and economic life. He is also the favourite of many in eastern Europe who still fear a rebirth of Russian imperial ambitions.