With 91 percent of the votes counted, election officials said Donald Tusk had won about 36 percent and Lech Kaczynski some 33 percent.
Tusk's Civic Platform party and Kaczynski's Law and Justice party both soundly defeated the ruling left in a general election two weeks ago. Their respective parties are in talks about forming a possible coalition, but there has been little progress due to the pending presidential election.
President Aleksander Kwasniewski, a former communist, has served two five-year terms. The constitution does not allow him to run again.