"I went to the door of the bar to see what was happening and a guy in a Croatian jersey came stumbling in with blood all over his face."
"One Croatian was being taken away by the police but then his friends started trying to stop it and there were around 15 fighting with the police.
"In the whole square there wasn't one Irish jersey so we started to panic but the riot squad formed a cordon and they threw tear gas.
"I've never seen anything like it. We didn't know how bad it would get so we just left the square altogether."
Many fans were unaware of the impending danger.
Salvador Flores who travelled from Mexico to support Ireland said: "It was a little bit scary. I have never experienced drinking in a bar surrounded by riot police. It was obvious that the Irish fans were just having a bit of fun but these guys were waiting there in a very threatening manner."
Shortly after 1am, police moved in to protect the hundreds of Irish fans behind a cordon of shields.
Despite the danger, the good-spirited supporters continued to sing Stand Up For The Boys In Green.
There were major fears that violence could develop after incidents earlier in the day saw a number of Croatian supporters injured.
Several hours before kick-off police were called in to stop a more significant fight.
The ugly scenes stemmed from an incident in the early hours of Sunday morning in which 10 Poles, three Irish and one Croat were arrested.
Around 100 riot police were forced to storm the square at 3.30am when fans started fighting.
An eyewitness told the Herald that "hooligans" wearing jerseys from the local Lech Poznan club arrived in the square where they attacked a group of Croatians from Zagreb.
Irish captain Robbie Keane's wife Claudine had been partying in the same area just a few hours earlier.
A police spokesman told the Herald: "At 3.30am on the square in the centre of Poznan there was a fight between supporters of Ireland and Croatia.
"The police were called in. We have detained 14 people.
"After we interrogate them they will all be allowed to go free. Nobody was hurt."
He said that the main concern of the police was "to find out is who was the first involved in this fight".
"I think our action will be to find out who was responsible.
"It was only a small incident. At this time there was 10,000 people having fun so 14 people being arrested is nothing."
Mayor of Poznan Ryszard Grobeln said he did not want the incident to distract from what has otherwise been a friendly atmosphere.
"The police action was swift and stopped it becoming a bigger event. I would not want to see any incidents of this kind happening," he said.
"But when you have thousands of fans and many litres of beer drunk these incidents are sadly inevitable.
"But we are very happy to have the Irish fans here, it is great to see so much of Poznan green at the moment.