Media Caption Petro Poroshenko and Volodymyr Zelensky held a long-awaited head-to-head debate at the Kiev Olympic Stadium in Kiev, in which Ukrainians will soon be taking part in a runoff election to elect the country's next president.
Voters are faced with a clear decision between incumbent President Petro Poroshenko and politically known television comedian Volodymyr Zelensky.
The TV star is popular in the polls He dominated the first round of voting three weeks ago, when 39 candidates were on the ticket.
Polling stations open at 08:00 (GMT 05:00) and closed 1
2 hours later.
A court in the capital, Kiev, refused a lawsuit in which it is required to detain Mr. Zelensky from standing.
One man had complained that the distribution of free tickets for a presidential debate by the candidacy of Volodymyr Zelensky was bribery.
On Friday, the two candidates appeared for the first time in the Olympic Stadium in Kiev to debate for the first time.
The TV event was the first time after a standard campaign in which Mr. Zelensky primarily used social media to communicate with the voting public.
The winner of the Sunday vote is elected President for a term of five years.
The position has significant powers in the country's security, defense and foreign affairs.
Who are the candidates?
In Ukraine, 41-year-old Zelensky is best known for his role in a political-satirical drama called Servant of the People.
- Ukraine competes with commercial knitting and media tricks
- Comedian in a rare stadium event
plays a teacher who accidentally becomes Ukrainian president after his chatter about the nation's politics in social media has become viral.
He is now running under a political party with the same name as his show.
With no political experience, his campaign has focused on its difference to others rather than concrete political ideas.
Nevertheless, he won the first round with more than 30% of the vote – almost twice as much as Mr. Poroshenko, when he finished second with 15.95%.
The incumbent president, in power since 2014, described the result as a "hard lesson".
Poroshenko, 53, is a billionaire who made his fortune mainly through his candy and television businesses.
] He was elected after an uprising overthrew the country's previous pro-Russian government.
The stadium debate between the candidates on Friday was eagerly awaited in Ukraine after the comedian had challenged the president to an unconventional event.
Following his acceptance, there was a public disagreement between the couple when it would take place.
Last week, Mr. Poroshenko appeared and debated an empty podium after his opponent was absent at the proposed deadline.
A leap into the unknown?
Analysis by Jonah Fisher, BBC News, Kiev
The Ukrainians have a choice whether to stick to what they have had in Petro Poroshenko for the past five years, or with the Comedy candidate Volodomyr Zelenksy make a leap into the unknown.
Mr. Zelensky is a well-known entertainer, but what he stands for politically did not become clear during the election campaign. However, he has proved that he can be a presidential leader – but only if he participates in a television series. 19659004] Ukraine is waging a war against the Russian-backed armed forces in the East, and President Poroshenko has repeatedly stressed the need for a politically experienced person.
Unfortunately, all polls show that Ukrainians are tired of their politicians regar as corrupt and in the pockets of rich oligarchs.
Important facts of Ukraine Source: CIA World Factbook