THE DVDs were pored over.

Paul Hartley sat through the footage of Celtic games under Ronny Deila and dissected them with a forensic eye. Dundee's manager made his players watch them too, including a final run-through not long before they emerged at a vibrant Dens Park yesterday. "We watched them for hours," said Hartley. "How we could hurt them. Even from the kick-off I said 'get it in behind them and try and turn them'." Hartley knew his gameplan, and there was a helping hand when Virgil van Dijk refused to play because Celtic would not let him leave.

The result does not show a Dundee win but Hartley and his players deserved all the credit. In this battle of the champions - Championship v Premiership - Dundee were more than Celtic's equal. Get in behind and turn them? Hartley's team did so time and again, especially with balls between Emilio Izaguirre and Jason Denayer. Celtic conceded once, to James McPake's header in the first minute, but their defending was seat-of-the-pants stuff throughout. Leigh Griffiths equalised with a deflected shot but their full-backs were too far upfield, the midfield gave away the ball too often, and the centre-halves had to make last-ditch tackles. Even then, Dundee would have won if they had more quality and danger up front. If Celtic's Europa League opponents do their homework as well as Hartley they'll be licking their lips.

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At Dens they were far, far too open and vulnerable. "We are disappointed at how many chances we gave them," said goalkeeper Craig Gordon. "But it's a work in progress. The manager is working on things." A penny for Gordon's private thoughts. A goalkeeper as good as him must have been horrified by the lack of protection.

Celtic were in trouble from the start. Dundee attacked down the left - as they would repeatedly- and won a corner. Phil Roberts' delivery was met by a powerful downward header by McPake, which bounced up and past Callum McGregor at the back post for a goal. Too easy. Roberts made a mess of Izaguirre down their right wing. What space Dundee found. Izaguirre and Adam Matthews, the Celtic full-backs, were pushed so far up that when Dundee snuffed out Celtic moves they immediately hit them on dangerous counter attacks. When Roberts beat Izaguirre again his low shot across goal might have crept in had Gordon not got the slightest touch to push it on to the outside of the post. Another Roberts delivery over the top put the ball into no-man's land between Gordon and Efe Ambrose. Miscommunication between them, and an odd bounce, allowed Peter MacDonald to steal in and almost score with a lofted shot.

Deila repeatedly urged his players to push up. Five minutes before half-time he replaced Jo Inge Berget with Griffiths, giving Celtic a 2-1-4-1-2 formation: centre-backs Denayer and Ambrose, then Biram Kayal, full-backs either side of McGregor and Stefan Johansen, then Kris Commons, then Anthony Stokes and Griffiths.

It was a top-heavy shape which could work only if Celtic were scoring, but too much of their play was in front of the Dundee defence and too many chipped forward passes were easy to intercept. Stokes and Commons were not firing. At half-time Deila made another change: Matthews off, Ambrose out to right-back/wing-back and Eoghan O'Connell on at centre-half.

There was more pressure and threat from Celtic at the start of the second half. Griffiths energised them, and he scored. He took a pass from O'Connell and rifled a low shot from just inside the box which took a deflection off Thomas Konrad to find a corner of the net. "I've seen him do it before," said McPake, his former Hibernian team-mate. "He hits the ball so cleanly. If you let him on to his left foot anywhere in from 40 yards you are asking for trouble."

Dundee were so deep they were inviting problems, but they were organised enough to frustrate Celtic. The game opened up again and Dundee re-emerged, getting in behind and turning Celtic. Martin Boyle raced through to thrash a shot at Gordon, and should have scored. Minutes later Izaguirre was too far up again, Boyle was in and he rode Denayer's challenge only to fire across goal and wide.

Celtic might have won it but Stokes' shot hit the outside of a post. This all made for a rousing match, but amid the range of reactions at full time it was impossible to miss the boos of some of the travelling support. The more discerning Celtic fans saw this for what it was: their team's weaknesses being exploited and their manager being outthought.