In his concession speech, Mr Tsipras said: “I wish and hope that the return of New Democracy to government will not lead to vengeance … particularly toward the significant achievements to protect the social majority and the workers.”
The snap election had been called after Syriza suffered a defeat in European elections in May, and became a showdown between Mr Tsipras and Mr Mitsotakis, who is set to follow in the footsteps of his father as prime minister.
Opinion polls prior to Sunday’s vote put New Democracy’s lead at around 10 per cent points ahead of Syriza, potentially giving it an absolute majority in the legislative house.
Mr Mitsotakis promised austerity-worn Greeks tax relief, stronger growth and a pro-investments stance. By contrast, Mr Tsipras, who clashed with the country’s official lenders and brought Greece to the brink of a euro exit in his fight to undo austerity, had ruled in a partnership with a small right-wing party and a thin parliamentary majority.
The poll was the first national election since the country shook off scrutiny from Brussels over the billions of euros loaned in three separate bailouts. Mr Tsipras signed up to the latest in 2015 in return for debt relief.
“The basic reason (for the result) is the economy,” said analyst Theodore Couloumbis. “In the past 4.5 years people saw no improvement, on the contrary there were cutbacks in salaries and pensions,” he said.
Mr Tsipras had appealed to young people to vote and “not leave the crucial decision for their lives and their future to others” after the voting age was extended to 16 for the first time in national elections.
But Mr Mitsotakis, the 51-year-old son of a former prime minister, brother of a former foreign minister and uncle to a newly elected mayor of Athens, managed to build a significant lead in opinion polls that held over the past three years.
He pledged to make Greece more business-friendly, attract foreign investment, modernize the country’s notorious bureaucracy and cut taxes, while fighting to shed the image of family privilege.
“Today voters take the decision for their future in their hands,” he said after voting. “I am sure that tomorrow, a better day dawns for our nation.”
Official projections based on early partial results also showed the extreme right-wing Golden Dawn party teetering on the lower side of the 3 per cent threshold needed to be in parliament. Golden Dawn became the third-largest party in parliament during Greece’s financial crisis.
Police said one ballot box was stolen from a polling station in central Athens moments after voting ended on Sunday. Authorities said a group of young people seized the box from a school in the capital’s central Exarcheia area, but there was no suggestion national results would be affected.
Additional reporting by agencies