Dublin - Martin O'Neill has vowed that the Republic of Ireland will bounce back from the worst defeat of his four-year reign when they begin their quest to reach a third European Championship finals in a row.
After holding Denmark scoreless last Saturday, Ireland were crushed 5-1 on Tuesday before a home crowd expecting a first World Cup qualification since 2002.
Ireland now have a long wait until their next competitive fixtures because the qualifiers for the 2020 European Championships do not begin until March 2019.
"We've lost a play-off game and we'll come back again," O'Neill promised.
"This is hard work and we've only been beaten four times in 24 competitive matches since I came in," added the manager.
O'Neill received plenty of flak of leaving Wes Hoolahan out in order to put the returning David Meyler back into a midfield diamond formation which played to the strengths of Denmark's hat-trick hero Christian Eriksen.
"We were well beaten in the end. Although we got off to a great start by scoring first, a second goal for us might have made a difference," said O'Neill who lamented the poor defending that enabled Denmark to take control of the second leg.
"We gave away two sloppy goals in the space of a few minutes and it was a long way back after that," said O'Neill.
"For their first goal, Harry (Arter) got beaten but we still be able to clear the ball and the second goal is just a comedy of mistakes.
"The whole mindset changes because six or seven minutes earlier, we could have been two goals up.
Denmark boss Age Hareide admitted he was hoping Ireland would adopt a diamond formation, and paid tribute to Tottenham midfielder Eriksen.
"I'd like to thank to you to Ireland," he said of O'Neill, Hareide's former teammate at Norwich City.
"Although they shut Eriksen out in Copenhagen, I couldn't believe the amount of space they gave him to exploit here in Dublin.
"The World Cup is about teams but also great players. It is beamed to a worldwide audience and Christian deserves to be on that stage showing the people what a world-class talent he is. Christian led the way tonight."
The Norwegian-born manager said he was always confident his team would recover from conceding an early lead to Shane Duffy's header.
"Our players kept their heads after going a goal down and their work paid off," he said.
"Conceding in the first five minutes is far better than conceding in the last five minutes... we had plenty of time to come back."