AN exorcism at Pittodrie brought back whispers from the past yesterday afternoon. As 10-man Aberdeen laid the ghosts of last season to rest by beating Celtic, the burgeoning sense that the Dons can be genuine title challengers was given substance by the manner of their victory over Ronny Deila’s side.

For the first time in their history, Aberdeen have won their opening six league fixtures. The significance of yesterday was not simply that it marked their most impressive start to a Pittodrie league campaign – a better start than any from the legendary Fergie years – but rather that it provided evidence that Aberdeen are capable of pushing for the title.

Inevitably, Derek McInnes was wary of talking up those chances. His conservatism may well be justified, but, privately, with no love lost between the Celtic and Aberdeen benches, he will feel his side have put down a considerable marker.

“It is still three points,” he said. “I know how important it is for that to be overcome [beating Celtic]. People who follow us see our determination and I think when you play against a level of opposition with Celtic’s quality, it is good confidence for everyone. You see how the supporters reacted at the end – the place was absolutely rocking.”

It was not just that McInnes’ side had the mettle to come from behind against a Celtic team that they could not beat last term, but how they did it. After taking the lead through a Leigh Griffiths penalty in the opening half, Deila’s side waited until the game was running away from them before showing any sense of urgency.

Griffiths had an effort in the final minutes of the game hooked off the line by Andrew Considine, but, by and large Celtic were outplayed by an Aberdeen side who did not look cowed by their visitors, and were disciplined and organised; Celtic were sloppy, disjointed and lacked fluidity. Even when Aberdeen were contentiously reduced to ten men when Jonny Hayes slid in on Mikael Lustig, Celtic could not make the advantage count.

With Virgil Van Dijk away to the Premiership, Celtic deployed Charlie Mulgrew and Dedryck Boyata at the heart of defence with Lustig on the right and on-loan Manchester United kid Tyler Blackett on the left. The back four once more looked uneasy dealing with crosses and set-pieces; Aberdeen’s winner came from a Niall McGinn free-kick – needlessly conceded by substitute Efe Ambrose – and while Craig Gordon ought to have been far more commanding in dealing with it, so too should the Hoops defenders. Gordon’s manager was not slow in acknowledging as much.

“We conceded a goal too easily from a set-piece,” said the Norwegian, who accepted that Aberdeen are now title challengers. “When Craig sees that he will say he should have come for that. I’m very disappointed with the result.”

The penalty which Celtic conceded and led to Aberdeen levelling the game was described as soft by Deila. While Graeme Shinnie certainly played for it, Boyata stood accused of gross stupidity. Neither Shinnie nor the ball were doing anything other than running out of play when Boyata barged into the back of him, giving Craig Thomson a decision to make. That it wasn’t the one which Celtic wanted – Nir Bitton and Scott Brown crowded the whistler at full-time to voice their displeasure – was an irrelevance. Aberdeen’s effort and endeavour ensured the scoreline, a direct reverse of that which kept Deila in the Celtic job last November, was fully merited.

What happens next is intriguing. Aberdeen play Hamilton on Tuesday evening – an opportunity to put further pressure on Celtic. Going five points clear at this stage of the season would ask significant questions of the tentative Hoops.

Questions, of course, will now be asked of Deila. The most pressing one at the minute is his choice of replacements when the game is going away from Celtic. Kris Commons remains arguably the club’s best player – and might have lent proceedings a spark – but was left cooling his heels on the bench in favour of the ineffective James Forrest and Nadir Ciftci.

Amsterdam comes calling this week for Celtic and defeat against Ajax will ensure difficulties for Deila. Jozo Simunovic was rested yesterday simply because he is just in the door and Deila believes he needs to acclimatise, but he will quickly need to fill that hole at the heart of the Celtic defence.

McInnes was right in that Aberdeen get only three points for the win. How much it spooks Celtic remains to be seen.