Far-right Austrian presidential candidate Norbert Hofer's campaign manager conceded defeat on Sunday to former Greens leader Alexander Van der Bellen.
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"The bottom line is it didn't quite work out," Herbert Kickl told broadcaster ORF as initial projections showed Van der Bellen leading with a score of around 54 percent to Hofer's 46 percent.
"In this case the establishment - which pitched in once again to block, to stonewall and to prevent renewal - has won," he said.
While the final result will not be official until absentee votes are counted on Monday, officials said the outstanding ballots will not change the outcome, even if the percentages of what the candidates won may vary.
The knife-edge presidential run-off was all the more dramatic for being a re-run of an election held six months ago - before Britain chose to leave the European Union and Americans elected Donald Trump as president - offering an indication of whether popular anger at the political establishment has grown.
When Norbert Hofer of the anti-immigration and anti-Islam Freedom Party (FPO) narrowly lost the original run-off in May with 49.65 percent of the vote, European governments breathed a sigh of relief.
That result, however, was overturned due to irregularities in the counting of postal ballots.
FPO's critics have accused the party of fascism since its establishment in 1956 by Anton Reinthaller, a former Nazi functionary and SS officer, with the party recently making headlines over the anti-Semitic rhetoric of some of its leaders.
Last year, the Freedom Party kicked out former lawmaker Susanne Winter for complimenting on Facebook a user who wrote: “The Zionist money-Jews worldwide are the problem.” In 2012, party chairman Heinz-Christian Strache apologized for posting on Facebook a caricature depicting an obese, hook-nosed banker wearing Star of David-shaped cuff links.
What influence Trump and Brexit have had on Austria is unclear, but the fault lines are similar - blue-collar workers have largely backed Hofer, the highly educated favor Van der Bellen.
Van der Bellen, 72, put Brexit at the heart of his campaign, arguing that Hofer wants Austria to hold its own "Oexit" referendum, putting jobs at risk in the small, trade-dependent country.
"It's a question of Austria being a firm member of the European Union or not," he told reporters after voting in Vienna, referring to the fact Hofer initially said Austria could hold its own referendum within a year, before backing down.
After casting his ballot in his eastern hometown of Pinkafeld, Hofer, 45, denied wanting to secede from the EU but did not explicitly rule out a referendum.
"I want to commit myself to changing this Union in a positive way and I don't want Austria to leave the European Union, that I have to say very clearly," said Hofer, who says he wants the bloc to be an economic rather than political union.
JTA and AP contributed to this report.