Late goals from substitute Andreas Laudrup and Emil Larsen helped Denmark get off to a fine start in UEFA European Under-21 Championship Group 4 as the visitors prospered despite the first-half dismissal of Mathias Jørgensen.
With a strong wind behind them in the first half, Denmark were ahead after six minutes, Nicklas Helenius converting Emil Larsen's corner at the back post moments after seeing a shot fended wide by Northern Ireland captain Chris Hegarty. However, Jørgensen was dismissed after 42 minutes, with Liam Boyce firing wide before the interval, and Josh Magennis being denied just after the break.
Steve Beaglehole's side almost levelled on 52 minutes when captain Oliver Norwood's thunderous long-range free-kick struck the woodwork before the Manchester United FC youngster tested goalkeeper Kristian Fæste with another set piece after the visiting No1 handled outside the box. Norwood struck the woodwork again on 80 minutes with a clever chip from 18 metres.
The game was killed off shortly after when Larsen got to the byline and put the ball on a plate for Laudrup – the son of Denmark legend Michael Laudrup – who steered home from 12 metres. Substitute William Grigg almost pulled one back on 86, but Denmark put the seal on victory in their first game since hosting the 2011 U21 finals when the influential Larsen fired into the bottom corner from 25 metres.