Mainstream parties and market analysts insist Tsipras cannot shred Greece's deal with 16 other eurozone countries and expect to remain in the single currency for long.
"(His) views only have appeal because of the exceptionally difficult circumstances this country and its people are in," Pangalos said.
Syriza came second to the conservatives in May 6 elections that failed to produce a government, winning nearly 17 percent of the vote and increasing its support four-fold.
Polls before a two-week pre-election ban projected Syriza's support could have surged to as high as 30 percent, with the race between Tsipras and the conservatives polarized by the crisis. Most have him neck-and-neck with the conservative New Democracy party.
Greece's €240 billion financial rescue from the EU and International Monetary Fund came with harsh conditions that have caused a dramatic drop in living standards as an average of 900 people have lost their job per day.
The country, Tsipras argues, is now trapped in a revolving door of debt, with banks recovering their money from new state loans from the EU, which steadily add a burden on ordinary Greeks, depriving them of wealth and services.
"Bankruptcy is not when the bankers have no money ... Bankruptcy is what we are living through today, it is the destruction of pension funds, it is hospitals running out of money and medicine, it is schools with no books and children who arrive hungry in the morning," he told parliament in February, when lawmakers slashed the minimum wage and other benefits to secure a second massive rescue package.
Fully named the Coalition of the Radical Left, Syriza is an amalgam of small and often fringe left-wing groups and has its roots in the Euro-Communist movement of the late 1960s. It is led by a party formed in 1991 that split from the hardline Greek Communist Party, or KKE, following the collapse of the Soviet Union.
As a teenager, Tsipras briefly joined the KKE youth.
Since the last major split in the Left two decades ago, Syriza has been a magnet for left-wing intellectuals unable to stomach the KKE's unconditional opposition to the European Union. Politically, however, most have spent their careers in obscurity.
Until now. At a recent campaign event, camera crews from around the world packed into an arts center where Tsipras spoke, as supporters chanted "The hour of the left has arrived!"
Embassy representatives from Cuba, Venezuela and France were present, as Syriza listed each of its campaign promises to loud applause: Axed benefits will be restored, troops will come home from Afghanistan and other overseas missions, police will be banned from using tear gas at demonstrations.
If he wins on Sunday, Tsipras left little doubt over his intentions.
"The first act of the new Left government, immediately after parliament is formed, will be to cancel the bailout terms and the laws passed to implement (austerity)," he said.
"People should remember that Greece is still a democracy: The voters elect their representatives, and they exercise their sovereign right to pass the laws of the land."
Copyright 2012 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.