For once, the weight of expectation proved too heavy at Celtic Park. A subdued, even unsightly, performance against Aalborg leaves Celtic with a colossal challenge to proceed from Champions League Group E.

They will require to garner at least six points from a daunting three-game sequence, starting in Villarreal at the end of the month. Thereafter, they face a defining and possible even decisive double-header against Manchester United, at Old Trafford on October 21 and Parkhead on November 5. Expect fireworks.

Gordon Strachan's side preserved the unbeaten run in group stage competition that stretches to the 3-1 defeat against Barcelona in 2004. They have also, crucially, preserved the less savoury statistic of never having won an opening group game.

It was fitting that a haphazard night ended with a case of mistaken identity as Aalborg slogged it out for the final 10 minutes with 10 men. Michael Beauchamp was the innocent victim of Matteo Trefoloni's incompetence. The Italian referee issued a straight red card to the Australian centre- back for a cynical foul on Georgios Samaras that was, in fact, perpetrated by Michael Jakobsen.

Regardless, Celtic could not capitalise on the advantage. They, or more specifically Barry Robson, had earlier squandered a penalty. For all their possession, they never looked like scoring against the Danish champions. One of Trefoloni's assistants was also hasty in flagging Scott Brown for offside as he tapped the ball beyond the otherwise unbeatable Karim Zaza. The only crumb of comfort was Manchester United's similar struggle down the M6 against Villarreal.

Bruce Rioch has cultivated a quietly industrious side and they successfully neutered the hosts. Thomas Augustinussen was a midfield anchor who kept his inexperienced charges on an even keel throughout.

Samaras, Shaun Maloney and, belatedly, Shunsuke Nakamura were exempt from the general malaise. Brown and Robson were buffeted about by Aalborg's athletic pack of players.

The greatest surprise in Celtic's line-up was the lack of surprise. Strachan, despite temptation, made only modest modification to the side that spanked Motherwell 4-2. Nakamura, emblematic of so many memorable European nights at Celtic Park, replaced Marc Crosas. Andreas Hinkel was favoured ahead of Mark Wilson. Hinkel, or Fankle as he will soon be better known, hardly vindicated his inclusion by threading a pass straight to an opposition player in the opening seconds. It was the start of another bamboozling performance from the German internationalist.

Maloney kept his position ahead of Aiden McGeady, who is still paying penance for a wasteful Old Firm display. Far too often, Celtic literally ran into trouble. It is a design fault that becomes pronounced at European level. As Aalborg crammed the central area with bodies, Celtic's wide players caused a bottle-neck.

Maloney, a right-footed left midfielder, and Nakamura, a left-footed right midfielder, were reliant on their full-backs over-lapping but that didn't materialise often enough and, when it did, the quality of delivery was deplorable.

Aalborg may be champions of Denmark but as they warmed up, they resembled a local high school team; callow to a man, or rather boy, and uniformally awestruck in this imposing arena.

Martin Pedersen, the Aalborg left-back, even dropped to his knees in anticipation of an unremitting bombardment. His prayers would be answered.

In contrast, Celtic possessed a masters degree in home Champions League football. Their experience rarely told. The atmosphere was typically riotous but there was an unusual bent to the bedlam. Tension made way for enthusiasm, hope made way for expectation.

Alas, such optimism was short-lived as Aalborg belied their pre-match nerves. They are unaccustomed to being anyone's superiors at this level and struggled with the concept. Celtic, so slick at the weekend, were stilted in their passing sequences.

Moreover, they were reckless in their defensive decision-making. Twice in quick succession Robson chopped down opponents like timber. His heart skipped a beat when Jakobsen smacked a free-kick just centimetres past Artur Boruc's goal.

Stephen McManus' recent fallibility was exposed when the supreme Augustinussen's agricultural pass looped straight over the centre-back's head. Jeppe Curth scampered to collect but stubbed his shot amateurishly wide.

Neither Robson nor Brown could gain a foothold in an over-populated midfield. Augustinussen was offered dead-bolt security before his back four and those in advance of the captain were obsessive in their tidiness.

The same could not be said of Celtic. Even their best chance was an accident. Hinkel, for once, found a team-mate. Samaras' head flick was received by the lively Maloney and, as he spun instantly, he was sent sprawling on all fours by Steve Olfers.

Robson grabbed the ball but bludgeoned the ball straight off the body of Zaza in a moment of blind courage. Samaras then reacted quickest in a penalty-box guddle but scooped over the bar to deepen the palpable frustration.

Celtic were evidently reinvigorated by a rollicking. Nakamura's vicious corner was fisted away on the goal-line by Zaza under intense pressure from Samaras, a beacon of hope amid the mediocrity.

The Greek deserved better for his efforts. He received a teasing pass from Maloney, spun his marker exquisitely and rolled his shot beyond Zaza's outstretched palm but also his left-hand post. It seemed destined to be that kind of night.

McGeady replaced a toiling Scott McDonald, which enabled Maloney to resume his developing partnership with Samaras; briefly, as it transpired, with Jan Vennegoor of Hesselink summoned for the late bombardment.

Nakamura's influence grew as Aalborg began to fade. He was uncharacteristically weak with a free-kick and marginally heavy with his incisive pass for a sliding Samaras. Nakamura then poked a pass through to Brown to tap in but the celebrations were premature as the far side assistant referee flagged frantically and, as it turned out, wrongly.