Ray Houghton has warned Ireland are in for a tough task in Denmark on Saturday night but thinks even a narrow defeat could be turned around back in Dublin.

Martin O'Neill's side are in Copenhagen for the first leg of their World Cup 2018 play-off tomorrow, with Irish fans optimistic after being drawn against the lowest-ranked of the four seeds (Croatia, Italy and Switzerland were the others).

Houghton, whose goal against England in 1988 was last night voted Ireland's Greatest Sporting Moment of the 1980s, warns against overconfidence however.

"What's happened far too often is we're under-playing the opposition," he told RTÉ Sport.

"It's as if everyone is delighted we got Denmark and it's going to be an easy task. Well it isn't, I can assure you.

"They got off to the worst possible start in their group. They had one win in their first three matches and after that they had five wins and two draws in the seven remaining games, so they're coming in to this game in real form.

"Christian Eriksen has scored six goals in his last six internationals, so he's really in form and could be the difference between the sides.

"I'm sure he's someone Martin will look at and hopefully have a plan in place to make sure he doesn't play to his very best."

Houghton doesn't expect O'Neill to alter what has often been an effective tactical blueprint of organised defence and direct counter-attack.

"I think he'll be pragmatic as usual," said Houghton.

"He'll take a lot of confidence from the victory in Cardiff against Wales. That was a hugely important moment for the team.

"They're apparently a team that tries to retain the ball. I think that will suit us.

"We're not a team that worries about when the opposition has got more of the ball than us but we have to defend well, and make sure we're very good in front of goal when we get the one or two chances we're going to create in the game."

The former Liverpool and Aston Villa midfielder thinks that the atmosphere the Irish fans can bring to the Aviva Stadium means any kind of close contest will be winnable.

"As long as we're in it. Even if we were to lose the game one-nil, with that Aviva roar on Tuesday and the crowd behind the players it would drive them on.

"The last two occasions that we've played away first in play-offs we've gone on to qualify so I think that all bodes well."

Live coverage of Denmark v Ireland on RTÉ 2 (7.25pm), live radio commentary on RTÉ Radio 1's Saturday Sport and live blog on RTÉ.ie from 6pm.