On the night that Celtic stuck four goals past Dundee United at Tannadice in the League Cup in mid-August, the devil lay in the details.

As impressive as Martin O’Neill’s men were on the front foot on that occasion, their defensive concerns were illustrated in Jim Goodwin’s men hitting the woodwork no fewer than five times.

It was no freak statistic either. In the 14 matches across all competitions which followed, the Parkhead men kept just four clean sheets and conceded 22 goals.

Sure, O’Neill’s men continued to grind out wins in the Premiership. But when any side continues to cough up chance after chance, you sense an accident waiting to happen.

That’s exactly what happened here. Celtic should have eased towards victory when Camilo Duran put them in front midway through the first half, but O’Neill’s side were woeful on the back foot for long spells thereafter.

Goodwin’s men capitalised fully before the interval, turning the game on its head through Zac Sapsford and Neil Farrugia. Had United a little bit more about them in the final third, they could easily have wrapped up a first win at Celtic’s home since Boxing Day 1992.

Credit where it’s due. O’Neill’s men improved after the break, although you might say it wouldn’t have been difficult.

While they deservedly levelled through Liam Scales and fashioned a string of half chances late on, they didn’t do quite enough to claim this as a hard luck story.

There’s so much that doesn’t convince about this Celtic side. Were it not for Duran’s eye for a goal, they’d be dropping points all over the place.

Kasper Hogh was selected from the start but didn’t re-emerge for the second half, his goalless run in green and white now standing at 13 matches.

Truthfully, though, the Dane’s was just one of a number of underwhelming displays for the home support to reflect on as they rued an opportunity lost to extend their lead at the top of the table.

There’s been an awful lot to admire about United lately. They arrived in Glasgow unbeaten in five matches with three wins in that run. The attributes of their midfield trio — Lyall Cameron, Zidane Iqbal and Dylan Tait — have complemented each other perfectly.

Some of their play — brave and creative — was outstanding. They defended manfully at the end when they had to and will feel the point they earned was richly deserved. It’s shaping up as a very promising season at Tannadice.

Although Celtic edged the early exchanges in terms of openings, so much of their play was lethargic.

Hogh did head a Kieran Tierney cross just over, although a nudge on Michael Forbes meant it wouldn’t have counted.

From Mika Baur’s short corner, Callum Osmand’s cross was met by Scales. The Irishman’s header drifted just wide.

United then served notice of what was to come in the later stages of the first half. From Cameron’s free-kick, Forbes’ header narrowly missed the target.

Celtic were struggling to get going. They lacked enterprise and energy. They were fortunate to find themselves in front on 19 minutes.

It was a well worked goal, the first cohesive move the home side had produced in the evening.

Osmand’s deep cross was kept alive by Scales. With his back to goal, Hogh had little choice but to lay the ball off. Duran was on hand to roll home his 11th goal of the campaign.

Given their effort to that point, United were entitled to feel hard done by. Lovely footwork by Iqbal left Duran for dead. Jesse Randall’s strike forced Sam Johnstone into a good stop.

Celtic responded. Osmand played in Hogh who found Nygren. The Swede’s strike was high and wide.

Osmand looked like Celtic’s best bet to open up United down the left. The forward cut an increasingly frustrated figure as his runs weren’t picked out.

United’s leveller on 28 minutes was no injustice. Cameron’s cross from the right was whipped in. Darting in between two defenders. Sapsford still had plenty to do. His headed finish was brilliant. That’s two goals in two games for the talented Australian.

Four minutes later, the visiting fans were in disbelief as their side went ahead.

Celtic never looked comfortable defending Cameron’s free-kick. Bert Esselink claimed it at the far post. Farrugia hooked the ball towards goal. Scales got a weak touch and Johnstone was far too easily beaten. Another shambolic defensive episode from O’Neill’s side.

The growing frustrations of the home side saw Colby Donovan booked for catching Sapsford late and Hogh also carded for dragging Iqbal back.

The first period concluded with Baur’s heading floating wide and Callum McGregor firing well over after being played in by Nygren. This was not going to plan.

O’Neill left Hogh and Osmand inside at the break. Jota and Haissem Hassan were asked to make the difference. Duran was moved to centre forward.

Jota did make a difference. With his first involvement, his quick feet played Baur in. The German’s shot didn’t trouble Jack Walton. Nor was the United keeper too worried when Jota stabbed a shot on target a few moments later.

Hassan had his moments too. He dropped a shoulder to cut infield from the left. His stinging shot forced Walton to tip it over the top.

Nygren then fired narrowly wide. But you sensed Celtic were stirring.

The equaliser stemmed from another set piece. Baur took a corner short to Jota. The Portuguese’s cross asked a lot of Scales. Despite the attention of two United defenders, he got first contact on the ball and guided a header home.

For a few minutes, United were reeling. Baur had a low shot brilliantly saved by Walton.

But the elementary errors soon returned to Celtic’s play. Johnstone did well to hold onto Forbes’ blistering low strike. The keeper also had to watch substitute Abdoulaye Yoro’s menacing drive all the way.

It all got rather chaotic towards the end. Having thrown every man up for a corner, Celtic were grateful that McGregor had the legs to get back and thwart Yoro.

Hassan had another run and shot which was deflected wide. Substitute Alex Oxlade-Chamberlain drilled an effort just the wrong side of the upright. Deep into stoppage time, Jota dropped a shoulder and saw his effort deflected wide.

Over the piece, a winner would have flattered Celtic.