By Steve Rosenberg
BBC correspondent in Moscow
To understand why Russia is so concerned about who wins Ukraine's election, take a look at a map of Europe.
Before 1991, Moscow controlled a huge swathe of land from the Pacific Ocean to the Balkans. It ruled 15 republics directly in the USSR. And, through the Warsaw pact, it held sway across Eastern Europe, too.
Russian president made it clear which candidate he supports
But the collapse of communism triggered the collapse of the empire. Since then, the European Union and Nato have enlarged right up to Russia's borders, taking in even former Soviet states like Latvia, Lithuania and Estonia.
One of Russia's other neighbours, Georgia, now has a pro-American government. Kyrgyzstan, another ex-Soviet state, hosts a US military base.
Russia feels vulnerable. Many here are still struggling to come to terms with the loss of empire. But President Vladimir Putin is determined to restore Russia's sphere of influence.
This is why Ukraine is so important: a country at the crossroads of Europe, bigger than France, and right on Russia's doorstep. Moscow is keen to keep Ukraine looking east.
So in this election it backed the man who promised to do just that - Viktor Yanukovych received the help of Russian spin doctors - and the very public support of President Putin.
Mr Putin visited Ukraine twice in the run-up to the vote, leaving no doubt which candidate he was backing.
He even invited Mr Yanukovych to his country residence outside Moscow. Russian television praised the Kremlin's choice, and Moscow was awash with election posters supporting him.
On Monday, President Putin's press secretary announced the Kremlin leader had telephoned Mr Yanukovych, and had congratulated him on winning the election.
A Georgian scenario for Ukraine is what Russia is keen to avoid
The aide reported Mr Putin had described Mr Yanukovych's win as convincing.
President Putin, it seemed, had become the first world leader to recognise Viktor Yanukovych's victory.
But 24 hours later in Portugal, the story had changed.
Yes, Mr Putin said, he had telephoned one of the candidates and he had offered his congratulations.
"We cannot yet," he said, "recognise or reject the results of the Ukrainian election since they haven't been officially announced."
It was, if not a U-turn, then at least an embarrassing clarification, and one which suggests that with events changing fast in Ukraine, Moscow may be trying to adopt a more balanced position.