Denmark coach Age Hareide thanked opposite number Martin O'Neill after a bold tactical choice backfired to give Christian Eriksen sufficient freedom to score a hat-trick and secure World Cup qualification.

The Danes booked their ticket to Russia with a brilliant 5-1 win in Dublin, Eriksen's treble sandwiched by a Cyrus Christie own goal and Nicklas Bendtner penalty after Shane Duffy had put the hosts into an early lead.

O'Neill forewent his usual defensive outlook, particularly in a second half in which his side needed to score twice, but it only served to provide Eriksen enough time and space to cut the Irish to ribbons.

The Tottenham star brought up 11 goals for the qualifying campaign with his exquisite treble although his coach admitted surprise that Eriksen had been afforded such an opportunity.

"It was very good, especially when we went 1-0 behind, we didn't get stressed," Hareide told Sky Sports.

"We tried to play, and we got the openings, and we got the goals. We were more effective than in Parken, the effectiveness is very important in football.

"I'm very pleased for the team, this is a difficult place to play football - they're compact and good defensively, so scoring five against Ireland does not happen very often.

"I was surprised. I think they played in a diamond with two forwards and that gave a lot of space in midfield for Eriksen and I just want to say thank you very much for giving him the space!

"They locked him down in Parken very well and Eriksen was more or less out of the game but today he was fantastic.

"He's always a fantastic player with the ball but also works hard for team all the time and he's an inspiration for all the lads.

"When you give him the ball, something happens, that's the difference between the sides - when you've got a world-class player.

"All the sides winning matches and in the World Cup have those kind of players."

Eriksen himself labelled the game as a highlight of his entire life.

The playmaker was the youngest player at the 2010 World Cup, where Denmark exited at the group stage, but more performances like this could see the Danes spring a surprise in Russia.

"It's an incredible feeling," he told Sky Sports. "We've been fighting for so long together after the two play-off games, which were very hard, but we got the result and we can be very pleased and I'm looking very much forward to World Cup.

"It's not often I score a hat-trick so of course it's incredible taking your country to the World Cup with three goals away in a play-off.

"It's going to mean a lot for my whole career, my whole life, so it's a big thing and I'm very happy about it."