Ireland needs at least a point from Thursday's Group C match against the defending champion to avoid an early elimination. But the team won't be short of support, with several thousand fans ready to deck Gdansk's PGE Arena in green, white and orange.
"We have just got to pray for a miracle — loaves and wine," said Joanna Faughnan, a fan from Dublin who bought tickets for all three group games. "Ireland always does well when people think we are down and out."
Having qualified for a major tournament for the first time in 10 years, Irish fans are making the most of the opportunity to party.
Thousands of fans poured into Poznan for the opening match and even a 3-1 defeat against Croatia failed to puncture the festive mood.
"It was incredible," Faughnan said. "The atmosphere was absolutely electric. Even after the final whistle the fans stayed and sang their hearts out."
Most observers expect Spain to steamroller Ireland. The reigning world and European champion has won 14 of its last 15 competitive fixtures and is bidding for an unprecedented third straight major international title. It will also be looking for points after being held to a 1-1 draw by Italy in its opener.
Still, Ireland only lost to Spain at the 2002 World Cup on penalties after forcing a 1-1 draw and there is a feeling among Irish fans that a courageous rearguard action could frustrate their illustrious opponent.
"I genuinely believe we will manage a draw," said Fionn Mac Aodhagain, from Rathcoole. "Obviously that's being very optimistic, but we have to believe. This time the luck of the Irish will be on our side."
Spain's players complained about the pitch in Gdansk being too dry during their previous match, a 1-1 draw with Italy.
"That won't bother the Irish," said Sean McCarthy, a fan from Westmeath. "We just kick it up in the air, anyway."
Despite a few arrests following scuffles in Poznan, Ireland's fans are generally managing to mix the alcohol intake with good behaviour.
So far, the rivalry between Spanish and Irish fans ahead of the match in Gdansk has largely been friendly and laced with the renowned Irish sense of humour.
Spanish fans dressed in red and yellow seemed to match the Irish for numbers on Thursday as supporters thronged the centre of the city ahead of kickoff.
A Polish couple who had just got married were also caught by the football fever, the groom donning a matador's hat and waving a red cape as his newlywed wife charged — and vice versa — to the cheers of watching Spain fans.
Bullfighting costumes were a particular favourite, with chants of "Viva Espana" ringing out around the city's main square to the accompaniment of drums and trumpets.
"We're going to win the group and now you're going to believe us," came the Irish response.
Ireland captain Robbie Keane has praised the support his team has received and sounded a defiant note ahead of the showdown.
"Most people have probably written us off and not given us any hope," he said. "But there's not a chance I would go into a game believing we are going to get beaten by anybody. It's 11 versus 11 over 90 minutes."
Mark Walsh can be reached at http://twitter.com/MAWalsh40Suggest a correction