Ireland is making just its second appearance at the European Championships, and its first in 24 years, but Sunday's Group C contest with Croatia is a vital one if The Boys in Green are going to have any hope advancing to the knockout round.
Both sides will be desperate for three points with the other two sides in the group, Italy and Spain, favored to advance.
Ireland is the clear underdog in the group with a roster that is inferior in terms of talent to those of the other three sides.
But Irish captain Robbie Keane thinks his team will wear the underdog tag well.
"Not many people will give us much of a chance this summer, but Ireland are at their best when they are written off," said Keane. "We did great to qualify for Euro 2012 and not many teams will enjoy playing us. The manager has made us tough to beat and we think we can cause a few surprises this summer."
Ireland will need strong goalkeeping from Shay Given and good play on the flanks from Aiden McGeady and Damien Duff in addition to a big effort from Keane.
A loss to Croatia on Sunday will make it extremely difficult for Ireland to find its way into the next round with two tough games still to play, while Croatia also knows how important it is to take three points against the Irish.
Croatia manager Slaven Bilic helped his team reach the quarterfinals of Euro 2008 before losing on penalty kicks, and he brings back a veteran side with plenty of playmakers, including midfielders Luka Modric and Niko Kranjcar.
Striker Nikica Jelavic is coming off a strong second-half campaign with Everton in the English Premier League and will team with Eduardo to give Bilic a potent attacking duo.
Bilic knows that his team is the more talented group on paper, but he feels as though Ireland manager Giovanni Trapattoni and his system and could be a bit of an equalizer.
"Trapattoni is the wildcard in this group as he will ignore the form guide," said Bilic. "We all appreciate how tough it will be to break down an Ireland side that works for each other in a very impressive fashion."