Rajapaksa's decision to call early elections in the hope of an easy victory over a fragmented opposition now appears a tough task with a broad coalition of parties rallying behind his former associate turned rival, Maithripala Sirisena.
Some 1,586,598 of the country's 21 million population are eligible to vote. About 1,076 polling stations have been set for elections.
A confident Rajapaksa had called the election two years ahead of schedule, hoping to win a record third six-year term before the defeat of the Tamil Tigers fades in the memory of
the people of the island which saw a three decades war over the demand of a separate Tamil Eelam.
Rajapaksa is popular among the 74 per cent Sinhala majority. He was regarded as hero for his military campaign which ended the LTTE's terror campaign in 2009.
The veteran politician was taken by surprise by the candidacy of former health minister, Sirisena, 63, who walked out of the government a day after polls were called.
That set off a wave of political turmoil and energised a long-dispirited opposition that had not been looking forward to the election.
Achala Jagoda became the 26th legislator to join the opposition unity candidate Sirisena in the endless stream of defections.
Both the president and his challenger belong to the majority Sinhala Buddhist community and much depends on how the minorities Tamils and Muslims vote in the elections.
The biggest Tamil political grouping has endorsed Sirisena's candidacy. Muslim parties concerned by rising violence from a range of hardline Buddhist groups which have emerged in recent years have also joined the opposition.
Grievances for Tamils include the continuing heavy presence of the Sri Lankan army in northern areas and a lack of local political autonomy.
In a bid to woo the Tamils, Rajapaksa campaigned in Vavuniya and appealed to the people there to vote "a known devil instead of an unknown angel".
The opposition campaign accuses Rajapaksa of nepotism, misrule, corruption and authoritarianism.
"I will end the Rajapaksa family rule," Sirisena said at his final campaign rally on Monday.
Rajapaksa's brothers - Gotabhaya and Basil - are defence and economic ministers respectively besides a number of his family members who are holding key posts and positions.
Elected first in 2005, Rajapaksa won a landslide in 2010 after bringing Sri Lanka's 26-year-old civil war to a conclusion.


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