Sunday's runoff vote in the ex-Soviet republic of 46 million people climaxed a bitter campaign of smears and insults exchanged between Yanukovich and 49-year-old Tymoshenko.
Five years on
Many commentators had predicted a narrow victory for Yanukovich, and analysts expect both sides to resort to legal manoeuvring and demonstrations.
Forced to step down in the Orange Revolution, the 59-year-old Yanukovich has enjoyed a narrow lead over Tymoshenko during the campaign.
The euphoria of the 2004 revolution has evaporated after five years of falling living standards and paralysing political squabbles between the president and the prime minister.
|Yanukovich ran a tight campaign and took care not to upset anyone [AFP]
"Yankuovich has learnt an awful lot in the last five years since the Orange Revolution," our correspondent said.
"Back then it was very much felt that he alienated voters in the west of the country - voters who looked towards the European Union for a future for the country - by mentioning the need to maintain strong ties with Russia.
"This time round he has refused to speak at all about anything that may be vaguely controversial. In the words of one analyst, he's played a secure campaigning game plan, making sure he doesn't put anyone off."
East or West
Yanukovich won 10 per cent more of the votes than Tymoshenko in the first round on January 17.
But his rival accused him of cheating after his Regions Party pushed through parliament amendments to voting rules after the first round.
The personal antagonism between Yanukovich and Tymoshenko mirrors the gulf between Ukraine's pro-Russian east and nationalist west.
Both candidates say they want to integrate with Europe while improving ties with Moscow, though Tymoshenko is seen as more enthusiastic about the European Union and Yanukovich is characterised as being closer to Russia.
Any challenges to the election results could stall Ukraine's political recovery and would likely delay talks with the International Monetary Fund on a $16.4bn bail-out programme derailed by breached promises of fiscal restraint.
Both candidates voted early, with Yanukovich narrowly missing a protest by four semi-naked women who forced their way into a Kiev polling station where he was to cast his vote.
The women, members of a small feminist group called Femen, were naked from the waist up and shouted: "Enough raping our democracy."