WARSAW — Liberal Warsaw Mayor Rafał Trzaskowski narrowly won the first round of Poland’s presidential election on Sunday against his right-wing rival Karol Nawrocki, setting the two up for a nail-biting campaign for the second round on June 1.

Trzaskowski, part of PM Donald Tusk’s Civic Platform party, won 30.8 percent of the vote while Nawrocki, supported by the populist right-wing Law and Justice (PiS) party, took 29.1 percent, according to an exit poll by Ipsos released on Sunday evening after the polls closed.

The projections are not official results, which will start coming in from Poland’s election authority in the next few hours.

Trzaskowski’s margin of victory was smaller than predicted in preelection surveys, giving Nawrocki momentum heading into the second round. POLITICO’s poll of polls predicted Trzaskowski at 31 percent and Nawrocki with 26 percent.

The Warsaw mayor now faces immediate pressure to broaden his appeal to a wider electorate, said Bartosz Rydliński, a political scientist at Cardinal Stefan Wyszyński University in Warsaw.

“We’re going to see pretty much cacophonous signals to all possible voters of other candidates bar Nawrocki,” Rydliński said.

This story is being updated.