“Do you know what a dark side is?” Woody Allen asks a female character in one of his movies (I think it’s Annie Hall). “I’ll tell you. When I’m reading a book, I always read the last page first, so that I know the ending, in case I die before I get to the end. That’s a dark side!”

Foul Play was brutally reminded of Woody’s words of wisdom on Wednesday night, watching Porto’s Clayton Ferreira Cruz stooping to plant a header into the Celtic net before even a full minute of play had elapsed. By then, we already knew the ending of this one, but we still had to sit there and take our medicine.

Was it that the Bhoys were utterly piss-poor, or that Porto were shit-hot? Only once have we seen Celtic get outplayed like that under Martin O’Neill, when Rangers gave them a right royal seeing-to (5-1) at Ibrox last November. The team then proceeded to win something like 18 of their next 19 matches, as if affronted by the margin of their defeat.

It may have been along these lines that a friend of mine was thinking when he greeted the sight of Porto’s fantastically well-worked third goal with the words, “By Jaysus, Dundee United are going to suffer for this one on Saturday.” At this stage, though, Foul Play is so used to seeing Celtic winning, and usually winning well, that the sight of them getting thoroughly dragged through the wringer was not so much dispiriting as genuinely startling.

Nonetheless, there are two points to be made here. The first is that this defeat, unappealing as it was to the eyes, has come too late in the schedule to fully destabilise O’Neill’s men.

Had Celtic kicked off their Champions League campaign with this result and performance, they would understandably be in ribbons psychologically. As it is, they had two wins on the board at the time of going to press, and were going into their away clash with Rosenborg as justifiable favourites.

Remember, we are talking about a club whose two most notable scalps in Europe since the early 1980s were 1.FC Köln and Tirol Innsbruck. Now they have beaten Ajax, Porto and Rosenborg in the space of two months. That’s progress in any man’s language.

The second thing to remember is that Porto are a startlingly good team, who would not look out of place in the last eight of this competition, for which they qualify on an annual basis.

It could, of course, be worse for Celtic. They could be in the position of Manchester United, who on the same night were denied a stirring victory over the best team in Spain by a goalkeeper who had seemingly left his brain in the dressing-room and his reflexes at another, undisclosed, location.

Fabien Barthez takes so many risks, most of them wildly unnecessary, during the course of an average game that I suppose it was inevitable he would eventually come to grief with costly results in a high-profile match. But I had always envisaged that when he did fuck up on a scale of this magnitude, it would involve trying to ill-advisedly dribble around an opposition striker, in the manner of Colombia’s Higuita at the 1990 World Cup.

Instead, he charges towards the ball and then decides not to clear his lines, while simultaneously making it impossible for Wes Brown to do it for him. 1-1. Then he again races out of his box, makes as if to handle the ball well outside the area, belatedly thinks better of it, and leaves it on a silver platter for Diego Tristán with the goal gaping. 3-2.

“Fab” will, however, live to mince around his penalty area another day. Not least because United’s alternative options are restricted to Raimond van der Gouw, who must be about 49 at this stage, and Roy Carroll, Norn Iron’s number one.

On the bright side, Ruud van Nistelrooy scored another couple of beauties, in the latest instalment of his ongoing battle with Juan Sebastian Veron to see which of them can most impress the United fans this season.

You would have killed for a Veron-esque flick or two in Kiev’s Olimpiyskyi Stadion last Tuesday night, as Liverpool defeated Dynamo Kiev in yet another dog of a game, in keeping with their previous performances in the competition.

Liverpool’s win over Kiev was slightly more watchable than their goalless draw with Dortmund, although that is not really saying very much. The unlikely star of the show, not for the first time in recent weeks, was Danny Murphy, who has latterly taken it upon himself to assume the mantle of centrifugal force in Liverpool’s midfield.

By all reasonable footballing criteria, Murphy is a bit of a donkey, yet here he is, popping up one minute to rescue the Pool against Leeds, materialising the next minute with a side-footed goal against Kiev. This has to say something either about the guy’s inner reserves of self-belief or about the general standard of English football. I’m not sure which.