What we learned: Ireland’s midfield keeps Danes at bay

Towering Duffy head and shoulders above

From the outset of Saturday night’s goalless draw it was clear Denmark knew it was going to be difficult to play through Ireland. As a result, their main tactic was to patiently build before launching long angled balls into the Irish box.

The Danes had two target men playing - Andreas Cornelius and Nicolai Jorgensen - while midfielder William Kvist would often drop very deep allowing fullbacks Peter Ankersen and Jens Stryger Larsen to bomb forward. The Dane's long ball tactic had some success - particularly early on as Larsen got in behind Cyrus Christie and forced a smart save from Darren Randolph.

However, Ireland were perfectly equipped to deal with the aerial bombardment - largely thanks to the presence of Shane Duffy. Duffy has flourished throughout the World Cup qualification campaign, and can now he considered Ireland's senior centre-half. He was relentless in the air in Copenhagen, winning pretty much everything launched his way. Along with Ciaran Clark, his distribution from the back is admittedly poor - but their cause is rarely aided by the Irish midfield.

Ireland pack the middle but can’t keep the ball

With Callum O'Dowda replacing David Meyler in a midfield three and Robbie Brady rarely foraging into the Danish final third Ireland effectively played with four central midfielders on Saturday night. O'Neill's decision to pack the middle of the pitch certainly worked when it came to frustrating Denmark, who were repeatedly unable to plot a route through the heavy white-shirted traffic in front of them.

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It also did a job in keeping Christian Eriksen quiet, with the Tottenham star rarely able to get on the ball between the lines and thus forced to drop deeper and deeper in search of possession. But despite having the numbers in midfield, Ireland's ball retention was simply abysmal.

Harry Arter and Jeff Hendrick - along with O'Dowda and Brady - were disciplined and dogged off the ball, but unable to keep possession when they won it. This is partly due to the fact Ireland were sat so deep that when they did see the ball it was normally well inside their own half, leading to a panicked clearance rather than a simple pass. A moment in the second half, where Arter won it well before hoofing aimlessly in the direction of Murphy - receiving an earful from O'Neill in the process - reflected Ireland's midfield efforts in a microcosm.

Long night for Murphy

Shane Long's goal-drought has been well documented, and there was no doubt Daryl Murphy deserved his place in the starting line-up on Saturday night. Murphy is a solid target man, and he brings a physicality to Ireland's play which Long can't offer.

However, in Copenhagen it was apparent just how valuable Long’s tireless pressing is to this Irish side. In games like this, when O’Neill sets his side up to sit behind the ball with next to no ambition in the final third, the centre-forward is handed a pretty thankless task. A night’s work involves a lot of pressing, a lot of chasing lost causes down the channels, and very occasionaly getting your foot on the ball - trying desperately to hold it up long enough for James McClean and Brady to join in support.

While Long has lost his eye for goal he is perfectly adept at this - he has the pace to pressure defenders. Murphy however doesn't have the legs of his impish counterpart, and on Saturday was unable to really press the Danish centre-halves. This gave both of them - particularly Simon Kjaer - plenty of time of the ball, allowing him to try and pick the diagonal passes the hosts believed were the best way to unravel Ireland. O'Neill has a big decision to make up front ahead of Tuesday.

Eriksen kept quiet

Much of the talk before the game concentrated on if, and how, Ireland could stop Christian Eriksen. Eriksen has been one of the standout players of the Premier League season so far - and is as valuable to Tottenham Hotspur as Dele Alli and perhaps even Harry Kane. But, for the most, part, Ireland did a job on him in Copenhagen.

With two solid banks of four sitting in front of the Irish box, Eriksen was rarely afforded the space he craves and which makes him so dangerous. Indeed, his best moment came from a glaring Irish error. Kasper Schmeichel cleared the ball long and Clark steered it perfectly into the path of the onrushing Eriksen, who carried before stinging Randolph's gloves with a shot from the edge.

It was a good sign for Ireland, though, that Eriksen began to drop deeper and deeper looking for the ball - with a number of hopeful pot shots from distance alluding to the frustration creeping into his game. Ireland’s defensive discipline was such it also meant Eriksen didn’t have a single threatening deadball situation to work with - another of his strengths. If Ireland can keep him quiet for all 180 (or 210) minutes of the playoff, they have a great chance.

Both sides escape final warnings

Of the 22 players who started at the Parken Stadium, 15 took to the pitch knowing a booking would rule them out of next Tuesday’s second leg in Dublin. It is a minor miracle that after such a hard-fought, scrappy game not a single player was cautioned.

Credit should go to referee Milorad Mažic, who was clearly sympathetic to the tightrope many of the players were walking and kept his book in his pocket throughout. In fairness, despite so much being at stake it was a fairly mild-mannered game and rarely reached boiling point.

Arter, however, can consider himself incredibly lucky to be available for the Aviva Stadium - his cynical tug on a breaking Kvist would have resulted in a yellow 99 times out of 100.