Opinion polls show Zeman winning the most votes in the first round of voting Friday and Saturday but too few to avoid a January 26-27 runoff with one of his eight challengers.
Czechs wrapped up voting on Saturday in the first round of a presidential election in which eight candidates are seeking to oust Milos Zeman, whose inclination toward far-right groups and warm relations with Russian Federation and China have split public opinion.
Czech presidents have limited executive powers but Zeman and his predecessors have had a strong influence on public debate.
Mr Zeman's victory is profoundly important to the recently installed prime minister, Andrej Babis, who heads up a minority government heavily dependent on the current president's support for its survival. Since then, he's been one of most prominent voices in Europe to call for abolition of sanctions against Russian Federation over the annexation of Crimea from Ukraine.
Zeman's policy preferences prompted protest action on Friday by a topless activist from feminist movement Femen who jumped in front of the president shouting "Zeman - Putin's slut" at a polling station where he cast his vote.
"As you can see, my security detail works quite well because she did not get to me", a smiling Zeman said upon his return.
First-round voting started at 2:00 p.m. (1300 GMT) on Friday and ends Saturday at the same time.
But the controversial populist could face a tougher threat from a single opponent in a run-off in two weeks if he does not win outright in the first round.
While the president may influence efforts to break a government stalemate as the cabinet is likely to lose the first confidence vote next week, Czech financial assets have been largely immune to political uncertainty. He regularly holds meetings with crowds in smaller towns.
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"I like that he speaks to voters", said Irena Matuskova, a Prague nurse who plans to vote for Zeman.
Zeman should do well in the first round due to fragmentation among opposition candidates sharing the same generally pro-EU platform. Among them, Jiri Drahos is the most likely candidate to advance.
Zeman's most serious challenger is Jiri Drahos, 68, a chemical engineer and former head of the Czech Academy of Sciences who has campaigned on anchoring the Czech Republic's place in Europe.
"I think President Zeman does not represent the country as he should", he told the BBC, "sometimes he behaves as if he were not our president, I'm ashamed".
Zeman has backed Babis even as the billionaire businessman has struggled to get support from other political parties while he battles police allegations he illegally obtained European Union subsidies a decade ago.
Political analyst Josef Mlejnek, from Charles University in Prague explained that Zeman's rivals are seeking votes from different strands of the electorate to him.
That message resonates with his supporters, even though virtually no Muslim migrants have tried to settle in the country of 10.6 million people.
Meanwhile, Mr Zeman's hardline approach to immigration from Muslim-majority countries has won him favour from large segments of the Czech public.
"What I would be afraid of is infiltration by jihadists, and thus a higher number of terrorist attacks in European countries or cities", he said on Thursday night in his weekly interview show, Week with the President, on TV Barrandov.