Only one old Glaswegian left here last night with a grimace on his face but then Sir Alex Ferguson has far too much at stake to appreciate the astonishing drama of Manchester United's defeat. His team have lost to Copenhagen and even Southend already this season but if you wanted a match that defied the pure logic of football then it was the one in the east end of Ferguson's home town.
Celtic were outplayed by United but it was the Scots who have reached the safety of the next round for the first time in the competition's modern format. Ferguson was left to reflect on how he will beat Benfica, who, with a devastating victory last season, denied his club a place in the second round - and how Louis Saha's nerve failed him when he could have rescued a point from the penalty spot in the dying moments.
United may have passed Gordon Strachan's team to death as the Celtic manager constantly changed his side to contain them, but they never created the chances to bury the Scottish champions once and for all. It would be hard to imagine Ruud van Nistelrooy missing a last-minute penalty however loudly Celtic Park bayed for him to fail and, for the first time since he departed in the summer, United missed their prolific Dutchman. Saha's controversial penalty, struck to the right of Artur Boruc, was arguably not even his worst miss, that had come earlier when he stopped with the goal at his mercy believing he had been flagged offside and then struck a weak shot at the Celtic goalkeeper.
"He thought he heard a whistle," Ferguson, who had flapped his arms in disgust at the time, later said in mitigation. Neil Lennon's suggestion that Gary Neville believed Saha's "head had gone" was more serious.
At the very best it was atrocious luck, at worst perhaps it said something more profound about United's ability to finish off teams, with an even more daunting task - Chelsea - awaiting them on Sunday. Ferguson said it was a good thing that United had so many big games to focus their minds but the significance of Chelsea's visit is rivalled by Benfica coming to Old Trafford on 6 December - and all the doomsday financial implications that accompany failure to make the next round.
Some game, though, especially after a first half in which Strachan admitted "we weren't even a presence". The question he set his players at half-time, was whether they wanted to be remembered for "that 45 minutes or the next 45".
When Shunsuke Nakamura's 81st-minute free-kick found the top corner of Edwin van der Sar's goal, even the Home Secretary, John Reid, in the Celtic crowd, could not stop himself from punching the air in delight.
United could not say that they did not know about the Japanese midfielder's potency with the free-kick, he scored a similar goal at Old Trafford this season. He got the chance this time when Nemanja Vidic fouled Jiri Jarosik on the edge of the area and the goal set off a remarkable conclusion to a game that had otherwise been short of goalmouth incident. Strachan said that he had not seen the penalty incident and saw no reason to watch it again but, had it led to United sharing the spoils, he would have felt differently. Cristiano Ronaldo, the game's outstanding player, struck a free-kick that hit Shaun Maloney around the elbow as he stood in the wall. The protests from the Celtic players were fierce and Lennon kicked the ball off the spot, Thomas Gravesen added his voice and both were booked.
Perhaps that was what "spooked" Saha as Strachan said, although he beat Boruc from the spot at Old Trafford on 13 September. There was something else that nagged about the match from United's point of view. They began with a baffling 4-5-1 system and Wayne Rooney little better than ineffectual on the left. When Strachan changed Celtic at half-time by bringing on Maloney and Jarosik, and switched to a five man midfield, he countered much of the threat of Paul Scholes.
United still dominated, but they never threatened to overwhelm Celtic even if their 53 per cent possession statistics looked like they should have been a lot higher. With 20 minutes left, Ferguson adjusted his team to play 4-4-2 and they seemed more dangerous. Strachan may have made mistakes with his selection but he rectified them more effectively.
A tactical victory for "wee Gordon", as Ferguson so often refers to him, over his old boss? He certainly made the best of a bad situation. Ronaldo's dribbling sequences took him past whole queues of Celtic players, but United so often overplayed when they could have been more direct.
Last season, the 2-1 defeat to Benfica in Lisbon, coming so soon after Roy Keane's impromptu departure, scarred United in a way from which they were never able to recover. They may yet win Group F but the alternative is too grim for Ferguson to contemplate. His back-handed compliment to Celtic was that they were probably "surprised themselves" by winning. Not as surprised as United will be if they find themselves out of the Champions' League next month.
Celtic (4-4-2): Boruc; Telfer, Baldé, McManus, Naylor; Gravesen, Sno (Maloney, h-t), Lennon, Nakamura (Miller, 85); Vennegoor, Zurawski (Jarosik, h-t). Substitutes not used: Marshall (gk), Wilson, McGeady, O'Dea.
Manchester United (4-5-1): Van der Sar; Neville, Ferdinand, Vidic, Heinze (Evra, 86); Ronaldo, Carrick (O'Shea, 86), Scholes, Giggs, Rooney; Saha. Substitutes not used: Kuszczak (gk), Brown, Richardson, Fletcher, Silvestre.
Referee: M Gonzalez (Spain).