The poll by the RAIT institute for the Baltic News Service gave the leftwing populist Labour party 19.8 percent and the centre-left Social Democrats 17.8 percent in the first-round vote. The two parties had already said they aim to form a coalition government.
The Conservatives did better than forecast, garnering 16.7 percent of the vote, the poll showed, while their Liberal Movement allies obtained 8.5 percent.
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Their performance pales in comparison to the leftwing parties even though Lithuania's economy has been growing since 2010, as they were blamed for undertaking a tough austerity drive well beyond those of western members of the European Union, which Lithuania joined in 2004.
"I would describe it as a very strong result and a kind of moral victory," Conservative Prime Minister Andrius Kubilius told Lithuanian radio.
Two other parties were shown clearing the five-percent hurdle for seats in parliament: the anti-graft Way of Courage movement, with 8.5 percent, and the rightwing populist Order and Justice party with 8.4 percent.
Seventy members of Lithuania's 141-seat parliament are elected by proportional representation from party lists in the first round. The remaining 71 are chosen in single-member constituency races, with two-candidate run-offs on October 28 where no candidate won a majority on Sunday.
Less than half the constituency seats tend to be decided in the first round.
But in past votes the final balance of forces has been sufficiently clear after the first round to enable the process of forming a government to begin right away -- even if the announcement of the ministerial carve-up follows the second round.
"The exit polls show there is no clear leader. There is a chance that the coalition will be made up of at least three parties. My prediction is that it will be the Social Democrats, Labour, and Order and Justice," Labour leader Viktor Uspaskich told AFP.
The Russian-born ex-minister and businessman -- best known for his gherkin business -- is a controversial figure, having been subject to a party funding probe and is highly unlikely to become premier notably.
He would not be drawn on who might get the job.
"It's too early to talk about the prime minister, we will wait for the second round. The Social Democrats usually do well in the second round," he said.
Social Democrat leader Algirdas Butkevicius is tipped to take the helm.
"We have worked with Labour and Order and Justice party for four years in opposition," he said.
"We need a strong majority," he told AFP.
The left-leaning parties pledge to raise the minimum wage and introduce a progressive income tax, but Butkevicius, a former finance minister, underlines his prudent credentials. He quit in 2005 when a Social Democrat-led government failed to close the gap between spending and revenue.
Kubilius -- the only premier to survive a full term since Lithuania seceded from the Soviet Union in 1990 -- ousted the Social Democrats in the last election in 2008.
His message then was that they let growth stoked by credit and wage hikes get out of hand and left the nation of three million ill-prepared for hard times.
Kubilius was premier in 1999-2000 when Lithuania was lashed by the economic meltdown in neighbouring Russia. But the 2009 crisis was far deeper, as Lithuania's economy shrank by 14.8 percent.
His government launched an austerity drive in response.
"We took responsibility for crucial decisions and guaranteed a responsible fiscal policy. I hope this responsible policy will continue," Kubilius said after casting his ballot.
Growth returned in 2010, at 1.4 percent, before hitting 6.0 percent in 2011, but analysts say too few voters feel the benefits, and emigration has spiralled. The government's forecast is a slower 2.5 percent this year, and 3.0 percent in 2013.
"I want change. I've suffered during the crisis. My salary was cut and my husband lost his job," voter Jurgita Kacinskiene, 36, told AFP.
Conservative voter Ramute Bacinskiene, 65, faulted that.
"It's not so bad here, we have food, clothes. We don't have wars here, look what's happening around the world. I believe stability is very important," she said.
The left also pledges to "reset" ties with Moscow, rocky since independence and spiking over alleged market abuses by Russian energy giant Gazprom, Lithuania's sole gas supplier.
