Left-wing politician Zoran Milanovic leads the field with nearly 30 percent of the vote in preliminary returns from Sunday's election.
Croatia's conservative president will face a liberal former prime minister in a runoff election after no candidate won an outright majority in a first round of voting Sunday, near-complete results showed.
Left-wing politician Zoran Milanovic led the field with nearly 30 percent of the vote in preliminary returns from Sunday's election. President Kolinda Grabar Kitarovic had almost 27 percent support, the state election authorities said after counting more than 95 percent of the ballots.
Right-wing singer Miroslav Skoro was in third place with around 24 percent.
The vote was held just days before Croatia takes over the European Union’s presidency for the first time. The ruling conservatives are hoping to keep their grip on power ahead of assuming the EU chairmanship.
Some 3.8 million voters in the EU's newest member country chose from among 11 candidates in Sunday's election, but only the top three finishers were considered serious contenders.
Milanovic and Grabar Kitarovic now will face each other in a second round of voting on January 5.
Although the incumbent finished second in the first round, analysts said Grabar Kitarovic could be considered a favourite in the runoff because other right-leaning challengers would no longer be in contention.
Despite the election taking place on a rainy day during the holiday season, election authorities said turnout was higher than during the last presidential election in 2014.
Some 100,000 more voters cast ballots by mid-afternoon compared to the same point on Election Day five years ago.
Croatia's presidency is largely ceremonial. The office holder formally commands the army and represents the country abroad.
But retaining the post is important for the ruling Croatian Democratic Union party, known as HDZ, as Croatia prepares for its six-month term in the EU presidency.
The job will include overseeing Britain's departure from the bloc, expected to take place on January 31, and the start of post-Brexit trade talks.
Grabar Kitarovic started off her campaign looking strong but her position weakened after a series of gaffes.
The 51-year-old incumbent is known for flirting with the extreme right while seeking also to portray herself as a peoples' president.
Milanovic, promised during the campaign to turn Croatia into a “normal” tolerant country.
Although Croatia has recovered since the devastating 1991-95 war that followed the breakup of former Yugoslavia, it still is one of the poorest nations in the EU and corruption is believed to be widespread.
The nation of 4.2 million people is best known for its stunning Adriatic Sea coast, which includes over 1,000 islands and picturesque coastal towns such as the medieval walled city of Dubrovnik.
Critics blasted the government for setting the election date three days before Christmas, a time when many people travel abroad.
The governing HDZ party, they said, counted on the support from Croats who live abroad and normally flock home for the holidays.
Analysts said the strong showing by the right-wing Skoro signalled that the governing HDZ had lost support among party followers ahead of a parliamentary election set for next year.