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O'Neill's men would fall behind to a contentious free-kick finish by Adam Cerin before being reduced to 10 men on the hour mark as Shea Charles was dismissed for a second bookable offence.

Northern Ireland were still lively with reduced numbers as George Saville would twice go close in the second half, although a lack of conviction in front of goal would, once again, be their downfall.

"Ultimately the free-kick decides the game,” said O’Neill. “I haven't seen the actual tackle but there was a delay in giving it which was strange from the official.

"That was probably the pattern of the game going forward for the night he was having.

"I think this is a learning curve for young players as they are much more experienced than we are...you can see that with how they managed the situation and they played the referee a wee bit.

"I think on the night we were pretty disappointed by the performance of the referee."

O'Neill believes the small margin of the defeat summed up their qualifying campaign to date, which has included five losses by a 1-0 scoreline. However, he has stressed the need for patience.

"I think the fans are always with the team," he said. "Northern Ireland are always going to go through difficult periods with results - their history tells us that.

"We've had a challenging campaign but we're probably at a point where it's the progression of a new team.

"It will take time because they are very young in a lot of areas…if you take Jonny Evans and Josh Magennis out of tonight, it's not a very experienced international team.

"You only have to look at our squad and the players who aren't here, I think the crowd knew it was going to be a very tough challenge to qualify.

"If you had five or six players it would have made it more achievable (but) there are things we can probably feel a little bit aggrieved about.

"These are lads that collectively aren't international players yet and we have to recognise that."

Northern Ireland manager Michael O'Neill highlights referee frustration