Sunday's poll in the respected Kathamerini newspaper said the New Democracy conservatives had a 5% point lead over Papandreou's Pan Hellenic Socialist Movement (PASOK).
The overwhelming backing for Papandreou, 51, far more than had been expected, and the latest poll sent mixed signals on where the March vote was headed.
The election, to be held six months before the Athens Olympic Games, pits inheritors of socialist and conservative political dynasties against each other.
The conservatives had held a7% lead in polls until support grew over the emergence of Papandreou as PASOK leader, cutting the lead to 3% points.
But PASOK has been hit by a land scandal involving its parliamentarians and fading euphoria over vows by Papandreou - a son and grandson of former prime ministers - to rejuvenate a party that has governed for 10 years and is attempting to win its fourth consecutive election.
"A cycle has closed. The country is ready for change," New Democracy leader Costas Karamanlis, 47, told a Sunday rally.
Karamanlis is the nephew of a former prime minister.
As part of efforts to give the party a new modern image, Papandreou's election as party leader - he was the only nominee - was sent to a vote by all party members as well as sympathisers rather than simply approved by party barons.
In a suprise result, more than 1,000,000 Papandreou supporters voted for him, seven times the number of 146,000 registered PASOK members.
There had been fears Papandreou's American-style party vote might have backfired as some saw it as a public relations ploy because the US-born foreign minister was the only candidate.
Authoritative sources said Papandreou would step down as foreign minister on either Tuesday or Wednesday to concentrate full time on the campaign.
PASOK won 157 of parliament's 300 seats in the last 2000 election.
Prime Minister Costas Simitis, 67, who led the party to victory in 1996 and 2000 elections, has voluntarily stepped down as PASOK chief and vowed to turn over the premiership to Papandreou if the party wins the election.