Croatia's centre-left rulers and the rival conservative bloc were poised to win an equal share of seats in parliament, an exit poll showed after voting finished.
A survey by the Ipsos Puls agency gave 56 seats each to the centre-left alliance led by the Social Democrats (SDP) and the conservative opposition bloc led by the HDZ party, the state-run broadcaster HRT reported after Sunday's vote.
Five other parties passed the five-percent threshold needed to enter the 151-seat assembly, according to the survey that polled 25,313 voters.
The third-biggest winner and likely kingmaker was Most ("Bridge" in Croatian), a newcomer on the political scene, which was predicted to take 18 seats.
The election came as the European Union's newest member grapples with a wave of refugees travelling through the country and an economy slowly recovering from six years of recession.
Prime Minister Zoran Milanovic of the SDP appeared to be hoping that his handling of the refugee crisis would help him stay in power, having disappointed voters after failing to press through reforms to revive the economy.
But the government's make-up is now likely to be decided in potentially lengthy negotiations with smaller parties.