Artmedia Bratislava came from two goals down to beat 2004 winners Porto 3-2 in their Champions League Group H match on Wednesday.
The defeat at the hands of the Slovakian team spoiled Porto's 112th birthday celebrations.
"We are a small city from a small country but we have a big heart," said Artmedia coach Vladimir Weiss, who dedicated the win to his sick father.
The home side went ahead after 32 minutes when Argentine midfielder Luis Gonzalez headed in a cross by winger Ricardo Quaresma.
Brazilian playmaker Diego made it 2-0 seven minutes later with a shot from inside the box.
Artmedia, making their Champions League debut this season, pulled a goal back through midfielder Peter Petras in first-half injury time.
The Slovaks silenced the 38,000 fans in the Dragao stadium when midfielder Jan Kozak equalised from a 54th-minute counter attack.
STRATEGY WORKED
Defender Balasz Borbely grabbed the winner when he tapped in a Kozak free kick with 16 minutes to go.
"We knew Porto's wingers attacked a lot so our strategy was to take advantage of it, working the diagonals," Weiss said. "Fortunately the strategy worked.
"Our first goal picked up the team's spirit and got them to believe in coming back. After that, in the second half, we scored two more goals and from then on we didn't let the win get away."
Porto's Dutch coach Co Adriaanse apologised to the fans for the defeat.
"I'm responsible and I feel ashamed Porto have lost on this birthday," he said. "We were well organised on paper but it's another thing to do it on the pitch."
Asked if he would change Porto's style in the next group match against Inter Milan, he said: "I'm not a coach that changes quickly.
"We were playing very well, I think we were dominating the game. Normally you win those games, why should you change your style?".
