He has strong support mainly in the countryside of the nation of 10.6 million people, and often snipes at Prague elites and the media.
Mr Zeman has become a vocal critic of the Euro bloc, railing against immigration, stoking the flames of Islamaphobia and encouraging closer ties with Russian Federation and China.
He leads eight other candidates, with around 41.3 percent of the votes, according to the results from half of the districts.
While the Czech Republic is the EU's richest post-communist member by economic output per capita - it also has the bloc's lowest unemployment and one of its fastest growth rates - Zeman has tapped into anti-migrant rhetoric resembling that of anti-establishment forces that scored gains in European elections previous year. A mild-mannered liberal centrist whom critics have dubbed "wishy-washy", he has called for Prague to "play a more active role in the EU" and has backed the adoption of the euro.
In one example in October, then Prime Minister Bohuslav Sobotka accused Zeman of interfering in Czech foreign affairs and contradicting the government when he repeated his stance against European Union sanctions on Russian Federation over the Ukraine crisis while defending Russia's annexation of the Crimean peninsula as irreversible.
As the results rolled in, analyst Jiri Pehe told AFP that "Zeman will have a huge problem in the second round".
Opinion polls show Zeman is the favourite but may face a strong challenge in the second round, expected in two weeks, where the two strongest candidates go head to head. The three pledged their support to Drahos in the runoff.
Horacek and Hilser showed up at Drahos's headquarters to shake hands, while Fischer also voiced his support.
As he voted in Prague on Friday, Zeman was targeted by a bare-breasted anti-Kremlin protester who called him "Putin's slut", referring to Russia's president.
Year-Old Survivor Of Texas Church Shooting Leaves Hospital
Some members of the Sutherland Springs community welcomed Ryland home as he passed through town on the fire truck. Duncan visited Ward in the hospital nearly every Sunday. "That's when I moved her and saw him".
After the polling stations closed on Saturday, the election commissioners will start counting the votes and send the data to the Czech Statistical Office (CSU). The 73-year-old is also seen as receptive to authoritarian regimes, while becoming one of Russia's most dependable allies in Europe.
Many voters remained undecided until the last minute, with Prague archivist Marcela Riegerova saying she "ended up tossing a coin to decide between two candidates, and Drahos came out the victor".
"I like that he speaks to voters", said Irena Matuskova, a Prague nurse who plans to vote for Zeman.
The outcome may influence Czech Prime Minister Andrej Babis's chances of finally forming a cabinet as his first attempt to rule in a minority administration is likely to be rejected by parliament next week.
Zeman was elected in 2013 during the country's first direct presidential vote, a victory that returned the former left-leaning prime minister to power.
But the situation could change dramatically if Drahos wins.
"In Czech we say that "the fish stinks from the head" and this perfectly sums up Zeman's presidency", he told the BBC.
Election officials said voter turnout was 61.9 percent in the preliminary election.