The dramatic withdrawal of the man who led Slovakia into the European Union and enacted far-reaching market reforms between 2002-2006 was a boost for Fico's socialist Smer party, which has ruled in coalition with nationalists and right-wing populists.
The euro zone's newest member since January 2009 is emerging from a deep recession but analysts expect ethnic tensions and accusations of corruption and cronyism rather than economic policy to dominate the campaign.
Dzurinda's centre-right government introduced a 19% flat tax on income and corporate profits which lured foreign direct investment worth billions of euros, notably in the auto industry. Fico advocates a strong state role in the economy but has departed little from orthodox policies.
"The key reason for me [not to run] was a monstrous game by Robert Fico," Dzurinda told journalists, denying the allegations and challenging Fico to debate them on television.
"I feel very sorry for him [Fico]. He has disgraced and insulted his post," he added.
Fico, 45, already favourite to win re-election, has repeatedly accused Dzurinda's SDKU party of money laundering and using tainted funds to finance its political activities.
"This evasive manoeuvre made by Mr Dzurinda today is pathetic," Fico told journalists after Smer's board meeting. "This is only a theatre, this solves nothing [...] We will continue to ask questions [about the SDKU's financing]."
Analysts saw SDKU significantly losing support.
"I expect this to have a marked impact on SDKU. Part of the party's electorate could desert to Freedom and Solidarity," said political columnist Marian Lesko of leading daily Sme, referring to a new opposition party which has similar policy aims to SDKU.
Slovaks enjoyed the fastest growth rate in the EU for years and reached a record 10.6% in 2007, but the global crisis took a deep bite, axing jobs and raising the fiscal deficit, seen back at the EU's limit of 3% of GDP in 2012.
Hungarian card
Fico came to power in 2006 teaming up with former autocratic Prime Minister Vladimir Meciar's nationalist HZDS party and the right-wing populist Slovak National Party (SNS), led by the firebrand Jan Slota.
Smer, led by Fico since its foundation in 1999, is hovering around 40% in opinion polls and holds a wide lead over centre-right rivals.
Strained relations with neighbouring Hungary, where conservative opposition Fidesz leader Viktor Orban is runaway favourite to win an April general election, will be among the top campaign issues, analysts say.
"Smer is using and will use the Hungarian card, it feeds distrust toward Hungary [...] this will be their evergreen," said Grigorij Meseznikov, the head of the Institute for Public Affairs, a think-tank.
The two countries' relations have never been rosy, due to the inclusion of a Hungarian minority - now over half a million people - into the newly formed Czechoslovakia in 1918. EU entry by both Slovakia and Hungary in 2004 did little to alleviate the ill-feeling.
Tension rose last year over a language law stipulating that only the Slovak language may be used in most public offices and institutions, seen by many as the latest in a series of moves by the nationalist-minded government to suppress their culture.
(EurActiv with Reuters.)
