The election, a re-run of a May 6 vote that ended in stalemate, amounts to a referendum on the punishing terms set by international lenders as the price of saving Greece from bankruptcy - withering tax hikes, job losses and pay cuts that have helped condemn Greeks to five years of record recession.
Riding a wave of anger to rise from political obscurity to contender for power, radical leftist SYRIZA leader Alexis Tsipras is threatening to tear up the terms of the 130 billion euro ($163.75 billion) bailout.
Tsipras says Europe cannot afford to cut Greece loose and cope with the fallout for the rest of the 17-member euro zone.
On the right, establishment heir and New Democracy leader Antonis Samaras says rejection of the EU/IMF bailout would mean a return to the drachma and even greater economic calamity.
Samaras told supporters on Friday they faced a stark choice - "euro versus drachma."
Neither party is expected to win outright, triggering coalition negotiations with smaller parties. A new government would buy time, but little respite. Whoever comes to power may find their tenure is short-lived.
Watch from Reuters: