The disturbances, which resulted in the arrest of 28 people, came at the end of a largely peaceful day of protest on Saturday as Ireland hosted the formal celebrations for the single biggest expansion of the EU in its 47-year history.
Violence erupted as a march organised by the anti-globalisation group Dublin Grassroots Network attempted to approach the Ashtown Gate entrance to the Phoenix Park from the Navan Road.
Rocks, bottles, beer cans and other missiles were thrown at gardaí when protesters were prevented from entering the park at around 8.30pm, where the heads of the 25 EU member states were sitting down to a ceremonial banquet at Farmleigh House.
Twenty-eight people were arrested at the scene and later brought before a special sitting of Cloverhill District Court at around midnight. Most of the 24 men and four women were detained for public order offences. Two Britons, a US and a Swiss national were among those arrested.
Twenty-one males were remanded in custody and placed in a wing of Cloverhill Prison which had been cleared of its prisoners earlier last week as part of a €4 million security operation. Four women were brought to Mountjoy women's prison, while three juveniles were released on bail.
Around 2,000 people, including members of the controversial British-based anarchist group The Wombles, took part in the march to the Phoenix Park, although the clashes with gardaí were largely confined to a small group of masked demonstrators.
A uniformed female officer was injured at the start of the violent exchanges, which lasted for almost an hour.
She was taken to James Connolly Memorial Hospital in Blanchardstown for treatment for minor head injuries but was discharged a few hours later.
Garda re-enforcements dressed in riot gear swiftly replaced ranks of ordinary officers following the outbreak of violence.
They were also supported by two water cannons which were supplied on loan by the PSNI.
As a result of Saturday's violence, a large garda presence is expected in Dublin city centre today for a "Reclaim the Streets" demonstration. It is expected to attract a large number of protesters, many of whom would also have attended other marches over the weekend.
Garda sources blamed Saturday's violence on a small group of hard-core activists intent on orchestrating a confrontation with the authorities.
The vast majority of people who took part in the march were not involved in any trouble, although a few minor scuffles developed between protesters and camera crews and photographers covering the event.
However, witnesses criticised the "heavy-handed" attitude adopted by some gardaí and claimed officers in riot gear had also hit out at people not directly involved in any aggressive behaviour.
"Gardaí certainly appeared to attack protesters quicker and in greater numbers than was necessary," said one person close to the violence.
Gardaí also expressed concern that a live shotgun cartridge, which is being technically examined, was found lying on the roadway at the scene of Saturday night's disturbances.
Garda spokesman Superintendent John Farrelly yesterday defended the reaction of the force, which he claimed was necessary to calm the situation.
"We had a job to do. The job we had to do was to protect society, to protect the people in the park and the situation was that has been achieved," said Supt Farrelly.
The conduct of the security authorities was also praised by Taoiseach Bertie Ahern. Speaking at a press conference with British Prime Minister Tony Blair at Government Buildings yesterday morning, Mr Ahern expressed disappointment that the Day of Welcomes had turned violent.
"It was a small band of deliberate troublemakers trying to mar a wonderful day. But they did not succeed in doing that," he said. He also complimented gardaí for the professionalism they had shown in the face of provocation by some protesters.
However, the Dublin Grassroots Network attributed blame for the May Day violence jointly on the Government and gardaí. The group claimed gardaí reacted disproportionately to "isolated pushing and shoving" when there was no real threat of protesters breaking through the lines of police.