His opponent, Deputy Prime Minister Jadranka Kosor, the candidate of the ruling Croatian Democratic Union (HDZ), gained 29.15 per cent.
Exit polls were conducted by the Puls and GfK agencies, covering about 20,000 voters at about 200 polling stations in the country. The surveys were based on data gathered by 5 p.m. and did not cover polling stations abroad.
Marijana Petir, spokeswoman for Mesic's election team, would not comment on the projections, saying that she was awaiting official results from the State Electoral Commission. She added, however, that the exit polls confirmed their expectations.
Kosor's election campaign manager Ratko Macek told reporters it was too early for comments.
The State Electoral Commission is due to release preliminary election results after midnight when the 48-hour campaigning ban expires.