Euro 2012 got under way on Friday, with Poland taking on Greece in the opening match, against a backdrop of fresh racism fears that risked overshadowing events on the pitch after a turbulent build-up.
Poland, who are co-hosting the tournament with Ukraine, kicked-off against the surprise winners of the 2004 competition in front of a capacity 50,000 crowd at the newly-built National Stadium, which was built on the riverside site of a former communist-era arena.
The streets of the capital Warsaw were a sea of Polish red and white, as European football's showpiece international tournament went behind the former Iron Curtain for the first time.
Holders and world champions Spain are favourites to retain the title, although perennial challengers Germany are out to avenge their final defeat from four years ago.
But the crescendo to the opening ceremony, a rich pageant of music and dance celebrating both countries' rich heritage, was overshadowed by claims that fans racially abused the Netherlands team during a training session on Wednesday.
Dutch skipper Mark van Bommel said in an interview published in De Telegraaf newspaper that the Oranje were forced to train away from the 25,000 fans who had turned up to watch in Krakow, southern Poland.
"We all heard the monkey chants," he was quoted as saying. "We can't accept that. We reacted well and the situation was sorted.
"During the tournament, if any one of us is confronted with such a thing, we'll immediately go to the referee to ask him to intervene," added van Bommel, who faces Denmark with his team-mates in Kharkiv, Ukraine, on Saturday.
Van Bommel's comments come despite a senior UEFA official previously denying there had been any racist chants and an angry response to a BBC programme last month which claimed far-right gangs were rife in Polish and Ukrainian football.
The documentary showed footage of some supporters making Nazi salutes and monkey chants at black players, as well as anti-Semitism and a violent assault on a group of Asian students.
Poland, Ukraine and UEFA president Michel Platini have all tried to play down fears of racist incidents, which prompted the families of two black England players to say they would not be travelling to watch the tournament.
"It's easy to point the finger at Ukraine and Poland for racism but all countries are faced with the same problem," Platini told reporters in Warsaw on Wednesday.
"We've done a lot of things but it (racism) is not a football problem, it's a social problem."
UEFA said on Friday that it was now aware of racist incidents, although it had not received any formal complaint from the Dutch football federation.
"Should such behaviour happen at further training sessions, UEFA would evaluate the operational measures to be taken to protect the players," it warned in a statement, without elaborating.
The Poland-Greece match in Group A is the first of 31 games in eight venues in the two eastern European nations, with the final to be played in the Ukrainian capital, Kiev on July 1.
Russia's Prime minister Dmitry Medvedev was later due to be in the stands in the western city of Wroclaw to watch Dick Advocaat's side take on the Czech Republic at 1845 GMT.