The vote is the first since the outbreak of the island's civil war in 1983 in which the Liberation Tigers of Tamil Eelam (LTTE) have endorsed a party, throwing their weight behind the Tamil National Alliance (TNA).
But that could also complicate matters if a government had to rely on the TNA for its power while at the same time was negotiating with the Tigers to permanently end a conflict in which more than 64,000 people have died.
"Whoever has to form the government will have to rely on the support of the smaller parties. What is the basis for that support? What price might they extract?" said Paikiasothy Saravanamuttu, head of the independent Centre for Policy Alternatives.
With the TNA projected to get 16 to 20 seats in the 225-seat parliament, and neither of the two big parties likely to win an outright majority, its backing could supply the winning margin.
The TNA would only ever be expected to give support to Prime Minister Ranil Wickremesinghe's United National Party.
"The TNA will in the early parliament support us on many issues, but they will sit in the opposition"
prime minister, Sri Lanka
But the other significant minority party in the house could be a Sinhala Buddhist party running an all-monk slate of candidates.
Projected to win between four and nine seats, they would be more likely to back President Chandrika Kumaratunga's
United People's Freedom Alliance.
Kumaratunga, who is not up for re-election, sacked Wickremesinghe's government in February, accusing her arch-rival of being too soft on the rebels.
"If you had a UNP government which had to rely on the support of the TNA in order to govern, it will be probably open to the charge of being held hostage by proxy to the LTTE," Saravanamuttu said.
Wickremesinghe said before formal campaigning ended on Wednesday that the problem would not arise.
"We're going to have a majority. The TNA will in the early parliament support us on many issues, but they will sit in the opposition."