With the majority Sinhalese vote split between Rajapakse and Fonseka, a close race is expected and Sri Lanka's 2.5 million battle-scarred Tamils could decide who wins the election on January 26.
Rajapakse and Fonseka have been on the campaign trail in the northern Tamil heartland of Jaffna -- a turn of events unimaginable a year ago, when fighting raged between the Tigers and government troops.
In the first four months of 2009 the United Nations estimates that 7,000 mainly Tamil civilians were killed in the fighting, while between 80,000 and 100,000 people died in nearly 40 years of bloodshed.
At their peak 10 years ago, the Liberation Tigers of Tamil Eelam (LTTE) controlled one-third of Sri Lanka. Rajapakse launched his push for complete victory in 2006, and Fonseka led the troops to triumph eight months ago.
The two candidates have sought Tamil support by promising to step up reconstruction in the former war zone and the speedy re-settlement of tens of thousands of Tamil civilians displaced by the final months of battle.
"The president moved about freely and spoke with the civilians," his spokesman said of Sunday's brief visit to Jaffna, while Fonseka addressed a rally in the region a week ago.
Victor Ivan, the editor of the weekly Ravaya newspaper, told AFP the Sinhalese community was still buoyant after the Tigers' defeat but divided over whether to back Rajapakse or Fonseka.
"The Tamil minority will be voting for the first time in 37 years without the presence of the Tigers," he said. "Tamils could decide the next president."
Major questions remain over the Tamil vote -- including whether many in the war-ravaged north and east are registered and able to cast their ballot, and who they might vote for.
Hundreds of thousands are still displaced and their turnout at the poll could be low, said Nimalka Fernando of the Movement for Democracy, a private advocacy group.
"Still, the Tamil vote will be a big factor," she said.
There is one independent Tamil candidate in the fray. But a group of Tamil parties known as the Tamil National Alliance (TNA), which has 22 seats in the 225-member parliament, announced last week that it supported Fonseka.
Moderate Tamil politician Dharmalingam Sithadthan said his community could act as kingmaker in the race -- springing the 12.5-percent Tamil minority into an influential position.
"Although the LTTE is dead, their influence could still be around. This means most of the Tamils could vote against Rajapakse because he is seen as the one who took the political decision to crush the Tigers," Sithadthan said.
The TNA, which was once seen as a proxy of the Tigers, called a boycott of the November 2005 presidential vote which was narrowly won by Rajapakse. Many believe the result would have been different had the Tamils voted.
The Tigers often used violence to stop voting and also carried out suicide bomb attacks and assassinations in the run-up to previous elections.
Fonseka, the architect of the military victory, quit in November accusing the president of sidelining him, and launched his campaign with a direct attack on Rajapakse's failure to deliver a "peace dividend".
Both candidates have promised to free thousands of Tamils still detained as Tiger suspects.
Political observers say corruption, the economy and media freedom are the central issues for the majority Sinhalese community, which is impatient to see the concrete benefits of victory.
Rajapakse called the election two years ahead of schedule in a bid to ride a wave of public acclaim after the Tigers' defeat and the killing of their notorious founder, Velupillai Prabhakaran.
But his row with Fonseka has presented him with an unexpected rival for power.