The Central Election Commission said that after ballots from 94 percent of the precincts were counted from yesterday's vote, the main challenger, opposition leader Viktor Yushchenko, had 39.14 percent against Yanukovych's 40.14 percent.
Yanukovych started the count with a commanding 67 percent advantage, but subsequent updates showed him consistently falling and Yushchenko rising.
The commission said turnout was around 75 percent.
Yanukovych, the pro-Russian candidate backed by Ukraine's ruling bloc, and the Western-leaning Yushchenko are now expected to face off in a second-round vote on 21 November.
Yushchenko's campaign said today its parallel count showed him ahead of Yanukovych about 46 percent-33 percent, with two-thirds of the precincts tallied.
Mykola Tomenko, a Yushchenko ally, said the opposition would "protect its rights" if Yanukovych won a fraudulent vote and announced possible "rallies, strikes, and demonstrations."
The Central Election Commission building was encircled by metal barriers and dozens of policemen deployed inside the compound were backed by water cannons and armored vehicles.
(compiled from wire services)[For full coverage of Ukraine's presidential elections, see RFE/RL's Ukraine web page.]