Trains arriving at the main station poured out waves of fans in the unmistakable red and white checks of Croatia chanting and blaring music, as groups of police looked on.
"We will win!" said Neno Cvetkovic from Osijek in eastern Croatia, just stepping off the train from Vienna with his two brothers, Croatian scarves and a flag hanging off his rucksack.
In town too, the streets were filled with dancing, singing and drinking Croatians, their rivals more than outnumbered.
"It's a peaceful party," said a German police officer with a smile, watching the partying fans. A few loud blasts in an isolated side street turned out to be just
Elsewhere, a group of Croatians refused to retaliate when a drunken German fan punched one of them, gently carrying him out of the crowd instead.
"It wasn't necessary to have all this police here. The media blew everything out of proportion," one cafe owner could be heard telling his customers. It's just a game, one team beats the other, that's it."
Some 2,500 police, including 400 Germans and 31 Croatians, were mobilised on Thursday in Klagenfurt to prevent any trouble.
Meanwhile, local residents continued to stay away from the city centre following media reports of fan violence and despite calls by local politicians to join in the celebrations.
"I think the Austrians are hiding," said Matej Zenz, 17. "The media reported a lot on Croatian and German fans and how dangerous it would be... I think it was all unnecessary panic," he said.
While the majority of the crowd had come for the football, Zenz and a few other youngsters held up banners pushing for more recognition of the Slovenian minority in Carinthia province.
"The Euro seemed like a good opportunity to get noticed," he said.
Fans turned out in the streets in even bigger numbers than Sunday when some 60,000 Poles and Germans descended on the sleepy south Austrian town for their
countries' first group stage match. But where rival fans met, good humour prevailed.
"We're looking forward to a great game, we hope we will win but it's ok if Croatia wins too," said Thomas Isermann, who traveled from Munich with 14 friends to see the game and "bring a little of the mood from the World Cup in Germany, to Austria."
That German fans were a minority in the crowd did not seem to bother him, as he shouldered an inflatable black German eagle, which he said was a statement.
"The message is have fun, peace, and football has the power to change the world," he said with a laugh.
Another German fan found the solution to inter-fan conflict. Faced with Croatian fans chanting "Deutschland, Deutschland, Auf Wiedersehen" (Germany, Germany, Goodbye), he encouraged his opponents to sing "Polska, Polska, Auf Wiedersehen," with him instead.
Germany and Croatia currently lead group B, ahead of Poland and Austria. Marko, from Senj in central Croatia, also insisted there would be no violence during or after the match.
"Do you see these people? It's all peaceful, people are coming together," he said. "Between Germans and Poles, maybe (there could be violence) but between Germans and Croats, we're friends, there's no reason for violence."
Some 28,000 Croatian fans and 5,000 Germans were expected for the game, including a number of violent supporters from both countries, according to Carinthia province police chief Wolfgang Rauchegger. Several people had already been turned back at the border since Wednesday, he added.
Klagenfurt police spokesman Gottlieb Tuerk told AFP the police had received "information about risk fans that we're analysing and evaluating. We're focusing on prevention," he added, noting however that "there is nothing to suggest there will be rioting."
At least 398 Croatian fans have been barred from entering Switzerland and Austria during the Euro.
On Thursday, five special trains as well as 50 Croatian and 65 German buses were expected to arrive in the south Austrian town. With Germany on the other side of the border and Zagreb just about 200 kilometres (124 miles) away, many also opted to drive to Klagenfurt.
On Sunday, 157 mostly German fans were arrested during the Germany v Poland game, but the much-dreaded violence otherwise failed to materialise.
On Wednesday, some 80 fans were arrested in Switzerland following violent incidents after the Switzerland v Turkey match, which saw the co-hosts eliminated from the tournament.