KIEV, April 21 (Reuters) - Ukraine entered uncharted political waters on Sunday after an exit poll showed a comedian with no political experience and few detailed policies had easily won enough votes to become the next president of a country at war.

The apparent landslide victory of Volodymyr Zelenskiy, 41, is a bitter blow for incumbent Petro Poroshenko who tried to rally Ukrainians around the flag by casting himself as a bulwark against Russian aggression and a champion of Ukrainian identity.

The national exit poll showed Zelenskiy had won 73 percent of the vote with Poroshenko winning just 25 percent.

If the poll is right, Zelenskiy, who plays a fictitious president in a popular TV series, will now take over the leadership of a country on the frontline of the Wests standoff with Russia following Moscows annexation of Crimea and support for a pro-Russian insurgency in eastern Ukraine.