Calzona’s team caused the first major upset of the tournament as Ivan Schranz’s seventh-minute strike rocked the Belgians in Frankfurt.
Although third-placed Belgium are placed 45 spots above Slovakia in FIFA’s rankings, the underdogs showed they were not overawed as they delivered an aggressive display that knocked Kevin De Bruyne and company out of their stride.
While Slovakia’s Group E upset is unlikely to be the start of a march to the final in Berlin, Calzona believes it should serve as a rallying cry to the unfancied teams competing in Germany.
“The smaller nations, the lesser teams if you will, have made progress and we can cause problems for the big nations,” he said.
“We have quality in the team. We’ve produced a number of excellent displays during the qualification stage. Of course it has an extra taste to it to beat Belgium. They are a top class side.
“It is true the small teams have improved. But there is still a big gap and we have to work hard. It is not easy.”
Slovakia will face Ukraine, beaten 3-0 by Romania on Monday, in their second group game on Friday, knowing a win would book their place in the last 16.
But Calzona, who served as Napoli’s interim coach for part of last season, cautioned his players against getting carried away by their success, which was aided by the controversial decision to disallow Romelu Lukaku’s late equaliser for handball against Lois Openda.
“It will be very tough to qualify. Unexpectedly the two teams who were favourites to go through have lost their first games,” Calzona said.
“They will want to get revenge but we don’t want to throw away this opportunity we have.”
It was a significant moment for Slovakia as they seek to emulate their run to the last 16 at Euro 2016.
They failed to get out of the group stage at the 2020 European Championship and Calzona said: “My team did what they had to do. We had to dig in during the second half but we showed no fear.
“I’m delighted. It’s a hugely significant win for me on a personal level. The lads are doing a great job and they deserved a success like this.
“Slovakia is a small country but so many people came to support us. To see men, women and children with a smile on their face was a touching moment.”
© Agence France-Presse