Greece's governing Socialists have won control of the capital, Athens, in the second round of local elections dominated by the country's debt crisis.
Prime Minister George Papandreou's Pasok party also won most races for regional governors.
Mr Papandreou said he had received a mandate from voters to press on with his austerity plan.
IMF and EU officials are due in Athens on Monday for talks on implementing a 110bn euros ($150bn;£93bn) rescue loan.
In Sunday's run-offs, Socialist-backed mayoral candidates won in both Athens and Thessaloniki - Greece's second-largest city - reversing a string of conservative victories dating back to 1986.
In addition, the Panhellenic Socialist Movement (Pasok) won eight of 13 races for regional governor - including in the greater Athens area.
Commenting on the results on Sunday, the prime minister said: "We have ahead of us a clear three-year period... to save and change Greece once and for all.
"We will put all our weight behind the major changes which will allow Greece to breathe, to stand up on its feet."
Pasok came to power last year. Its parliamentary mandate expires in 2013.
Last week Mr Papandreou dropped his threat to call a snap general election after Pasok avoided heavy defeat in the first round of regional elections.
New figures also due on Monday are expected to show Greece's budget deficit for last year was worse than previously declared.