Based on partial results of the provincial councils on Monday, the anti-immigrant party picked up 7.6 percentage points to reach 20.8 per cent across northern Dutch-speaking Flanders and surged well beyond its traditional stronghold of Antwerp.
Yet, opponents point to Antwerp, the cradle of its popularity, where the party suffered its only sizable setback, dropping to second place behind the Socialists of incumbent Patrick Janssens, the mayor.
The mayor's personalised campaign gave the Flemist Socialist Party (SPA) 35.3 per cent of the vote, almost double the 19.5 per cent it won in the last election six years ago, while Flemish Interest only added half a percentage point to 33.5 per cent.
The "symbolic defeat" of Vlaams Belang in Antwerp "was more important than its progress in the rest of Flanders", said Pascal Delwit, researcher at the University of Brussels.
The party has "perhaps reached its ceiling", he said, notably given that it lost four percentage points in Flanders from the last general election in 2004.
The Belgian media also welcomed Vlaams Belang's failure in Antwerp.
"Antwerp deserves better than the far right ... Belgium can breathe again," wrote Beatrice Delvaux, editor of the newspaper Le Soir, whose front page headline was "Stop right there!"
Flemish-language newspapers hailed the victory of Antwerp mayor Patrick Janssens and his Socialist party (SPA).
"Janssens stops Belang" and "Janssens brings Vlaams Belang to a halt", blared headlines in the newspapers Het Laatste Nieuws and De Standaard respectively.
Another factor may have been a racist killing in May in which a skinhead gunned down an African woman and a white child in her care, sparking anti-extremism rallies.
The poll was also a blow for Guy Verhofstadt, the Belgian prime minister, whose Flemish liberal democrat VLD won 19 per cent of the vote in Flanders, compared to 32 per cent for the opposition Christian Democrat CDV.
Dewinter's Vlaams Belang failed
to seize control of Antwerp
In advance of the elections, CDV party figurehead Yves Leterme sparked anger in Wallonia by calling for more powers to be devolved to the Flemish north.
Where the far-right party lost or stabilised, party leaders blamed it on immigrants, arguing that a quick naturalisation process approved over the past years allowed the newcomers to dilute its popularity.
Looking at the whole of wealthy Flanders, home to six million of Belgium's 10.5 million people, the latest surge of the Flemish Interest party was unmistakable.
It was an indication that voters were drawn by the party's recent attempts to tone down its hard-line image and by its ability to connect with people's everyday concerns in a country where politicians often seem aloof from the worries of the common man.
Despite its strong showing, it was seen as unlikely that the party would be able to transform its support into governing power, because other parties on the local level have in the past formed coalitions to keep it from taking control of city councils.
The party attributes its success to efforts to tap into concerns over a perceived rise in crime, degradation of inner-city neighbourhoods, and an increase in asylum seekers and illegal immigrants.
The party made big gains in nearly all the 308 municipal councils across the northern Flanders region.
Expanding its support base beyond Antwerp, the party won the most votes in seven municipalities outside of the northern port city.
In many places, the party won more than a quarter of the vote, according to early results.
The Flemish Interest party, which was forced to change its name from Flemish Bloc two years ago after a ruling on racism by a national court, has sought to project a more moderate image.
The party, which had already taken hold in the major cities of Flanders, rose sharply in villages and small cities on Sunday.
For years, Belgium's traditional parties and much of the mainstream media have been doing their utmost to contain the spread of the extreme right.
They have ostracised the party, heaping one Nazi metaphor on top of another, successfully taking them to court on racism charges and entering unlikely coalitions to keep them out of government.
Sunday's vote was the biggest win for the party since it first emerged on the political map two decades ago.