Rivals from Ukraine's Orange Revolution are considering reuniting to keep out a pro-Russia party leading parliamentary elections with half the votes counted.
Yanukovych, Tymoshenko and Yushchenko have hopes of power
President Viktor Yushchenko's party is running only third with 16.3% of the vote, the Election Commission said.
Correspondents say he may join ex-ally Yulia Tymoshenko, currently second with 23.4% to the 27.3% of former PM Viktor Yanukovych's party.
Mr Yushchenko's chief-of-staff said any coalition talks would take time.
Ms Tymoshenko said Mr Yushchenko had agreed to meet her on Tuesday. "I have not seen the president for a long time and we have a lot to discuss," she said.
'Free and fair'
The Election Commission has announced the half-way situation, giving the narrow lead to Mr Yanukovych's Party of Regions.
Ms Tymoshenko's bloc is second, followed by Mr Yushchenko's Our Ukraine party.
The Socialist Party and the Communist Party have both crossed the 3% threshold needed for parliamentary representation.
A total of 45 parties were on the ballot papers.
Full counting is not expected to be completed until Tuesday.
Observers from the Organisation for Security and Co-operation in Europe have described the election as "free and fair".
A victory for Mr Yanukovych - who was written off a year ago - would be a dramatic comeback.
He was declared the winner of the presidential election in November 2004, but allegations of widespread vote-rigging sent hundreds of thousands of Ukrainians out on to the streets to demand change.
In what became known as the Orange Revolution, the election result was overturned and Mr Yushchenko went on to win a re-run.
If confirmed, the results would be a humiliating blow for Mr Yushchenko, whose popularity has plunged following a year of political infighting and sluggish economic growth.
Support for opposition leader Viktor Yanukovych has grown
The president fell out with some of those who stood beside him on the stage in Kiev during the revolution, including his prime minister, Ms Tymoshenko, who was sacked.
Now it looks like the pro-Western liberals will join forces again, but this time Ms Tymoshenko is in a commanding position, the BBC's Helen Fawkes reports from Kiev.
Mr Yushchenko's chief-of-staff, Oleh Rybachuk, told the BBC's Newshour programme that so far the two sides had done little more than announce their intentions.
"I do not expect any formal agreement signed, neither today nor in the nearest future," he said.
Mr Rybachuk's deputy, Ivan Vasyunyk, added that it would be premature to finalise any coalition deal before official results are announced.
Ms Tymoshenko has said she wants to return to the post of prime minister.
She has also vowed to cancel a controversial gas deal Ukraine signed with Russia.
Both of these proposals would be difficult for Mr Yushchenko to accept but he has been left with few options, our correspondent says.
Mr Yanukovych was also trying to tie up a coalition, urging smaller parties to team up with him to see off the liberals.
"Today's victory is a revelatory moment for both myself and the Party of Regions," he said.
"It has shown that despite everything, the people have managed to show their great support of our political force."
Mr Yanukovych said he would support ties with the European Union, as well as mending Ukraine's relationship with Moscow.