Incurring the displeasure of Sir Alex Ferguson, as Alex McLeish is well aware, has consequences. The Birmingham boss, like Ferguson's former charges, has felt the fearsome force of 'the hairdryer treatment' before when the then Aberdeen manager's fuse was still shorter.
Now, victory notwithstanding, his ire was reserved for his current side, with neither the New Year nor Ferguson's 66th birthday seeming to improve his mood. Both the Manchester United players and supporters found themselves chastised after brilliance was coupled with complacency at Old Trafford.
'I was concerned,' Ferguson said. 'We were careless.' Indeed they were careless, both in the squandering of chances and in their attitude to preserving a 1-0 lead. 'You can't do these things. But the crowd were dead. That was the quietest I've heard them. We needed the crowd today. We needed a good atmosphere and the players need the crowd to respond and vice-versa. Today it was like a funeral, it was so quiet and I don't think that helps us.'
The crowd can consider themselves rebuked but the players have more immediate cause for concern. Of the five changes from the side beaten at West Ham, there was no pretence that Louis Saha, Darren Fletcher or Wes Brown were rested. There are further candidates for positions on the bench or in the stands at Aston Villa on Saturday in the FA Cup after United allowed the Second City's other side back into the game. To complete an undistinguished few days, the champions were insufficiently ruthless. The win could, and should, have been wrapped up long before Birmingham rallied in the final 20 minutes.
Two of the culprits, who nonetheless conjured a goal of sheer class, were Carlos Tevez and Cristiano Ronaldo. The Argentine found his ersatz strike partner with an overhead kick and Ronaldo completed an unconventional one-two with a backheel before Tevez slipped the ball past Maik Taylor.
'It was a fantastic goal, absolutely superb,' added Ferguson, just about the only compliments he paid in his post-match interview. Birmingham were appealing for a free kick after Rio Ferdinand's challenge on Cameron Jerome but, to his credit, McLeish refused to use that as an excuse. 'It's a centre forward who was out of the game anyway,' he reasoned. 'It's what happened next that's most important and I don't think we handled it well.'
While one Alex emerged with the points, the other merited rather more plaudits. 'We know that United have got individual brilliance that can change a game,' McLeish added. 'The players were very disciplined. We're realistic when you're pitting your wits against Sir Alex, it's like a water pistol against a machine gun. He's got £125million of talent out there. Our intention was to take something back to Birmingham. We had to have a gameplan.' That plan could have come to fruition.
The theory that, provided a team restricts the deficit to one goal, it can provide the platform for attacking substitutions and a late onslaught, is often heard. This provided that rarity of an occasion when it almost worked.
With a quarter of the game remaining, McLeish introduced Daniel de Ridder and Mikael Forssell, who became Birmingham's major attacking threats. The Finn, looking ominously sharp, produced a series of shots and only missed the target narrowly.
A previously underemployed defence became rather busy. Yet, for several reasons, they should not have been required. Tevez had struck the post at either end and Ronaldo drew a fine block from Taylor, but United's problems stemmed from their difficulty in closing out a game they appeared to believe they had already won.
Perhaps a glance at the statistics had contributed to their false sense of security. That Birmingham have mustered a solitary draw this season against teams in the upper half of the Premier League is an indication of the increasing gulf in class in the division, but they were unusual among visitors to Old Trafford in displaying the belief they could pilfer a point.
Once again, that should be attributed to McLeish. Under Steve Bruce, Birmingham appeared assured of defeat at his old club. The new incumbent at St Andrews didn't confuse respect for his mentor with a reluctance to challenge his team.
Ferguson, as his post-match comments showed, remains abrasive as ever and as willing to confront and criticise his own. Experience has taught McLeish that he is a hard taskmaster, but some of Ferguson's current charges played as if they were unaware of that. They might not be for much longer.
MAN OF THE MATCH: Maik Taylor - Made a series of saves with one, from Ronaldo, that was absolutely superb.
MANCHESTER UNITED VERDICT: In his absence - for the majority of the match, anyway - United displayed why Owen Hargreaves is essential to add steel in the centre of the pitch. The more encouraging contributions were provided by Ji-sung Park and Nani, lively on either flank, though United could have benefited from either displaying a cutting edge. Ronaldo, prolific on the wing, failed to score as a striker.
OUT OF THE CUP: Carlos Tevez appears likely to miss the FA Cup tie at Aston Villa with the ankle injury that forced his withdrawal. 'He's a tenacious little lad, brave as a lion,' said Ferguson, indicating the striker could not continue. Wayne Rooney, however, is likely to return.
BIRMINGHAM VERDICT: While McLeish looks for both quantity and quality in the transfer window, Birmingham played with a spirit and an organisation that some of their relegation rivals should envy. They may be one of the three least talented teams in the division but, under McLeish's guidance, they should survive.
SCOT FREE? There has been the assumption that McLeish, like several of his compatriots, would start his recruitment drive north of the border. Not so, according to the Birmingham manager, hinting that he shouldn't be underestimated. 'I'm quite knowledgeable in terms of European players and players across the world. My knowledge of England is half decent, so it doesn't necessarily mean I'm bringing in Scottish players.'