Radu Magdin, a political commentator, said the difference between his single-digit popularity and Sunday’s result was without precedent since Romania shed communism in 1989.
“Never in our 34 years of democracy have we seen such a surge compared to surveys,” Mr Magdin said.
Campaigning focused largely on the soaring cost of living, with Romania having the EU’s biggest share of people at risk of poverty.
Ms Ciolacu had courted voters with a promise of generous spending and no tax rises, despite Romania running the European Union’s largest budget deficit at 8 per cent of economic outlook, while offering a sense of security in policy stability at a time of a war next door.
Mr Georgescu, formerly a prominent member of the hard-Right Alliance for Uniting Romanians party, has called Nato’s ballistic missile defence shield in the Romanian town of Deveselu a “shame of diplomacy”.
He has said Nato will not protect any of its members should they be attacked by Russia.
“We are strong and brave, many of us voted, even more will do so in the second round,” Georgescu said on Sunday, outside a residential building near Bucharest, Romania’s capital.
Defence spending
Ms Lasconi, a former journalist, joined the Save Romania Union (USR) in 2018 and became party head this year. A two-term mayor, she believes in raising defence spending and helping Ukraine.
Romania shares a 400-mile border with Ukraine and since Russia attacked Kyiv in 2022, it has enabled the export of millions of tons of grain through its Black Sea port of Constanta. It has also provided military aid, including the donation of a Patriot air defence battery.
Villages on the border with Ukraine have seen a barrage of drones breaching national airspace, although no casualties have been reported.
One political commentator said Russian meddling to give Mr Georgescu an edge could not be ruled out in the election.
“Based on Georgescu’s stance towards Ukraine and the discrepancy between opinion surveys and the actual result, we cannot rule [that] out,” said Sergiu Miscoiu, a political science professor at Babes-Bolyai University.
Klaus Iohannis, 65, the outgoing two-term president, has cemented Romania’s strong pro-Western stance but was accused of not doing enough to fight corruption.
Sunday’s result is one of the biggest surprises in Romanian post-communist elections, with the leaders of the two largest parties, the Leftist Social Democrats and centre-Right Liberals, which are in a coalition government, eliminated in the first round.