Threadbare Sunderland squad is O'Neill's undoing

There is something quite unsettling about the habit of those players Sir Alex Ferguson sells to bear gifts when they return to Old Trafford. Manchester United's rivals always scent a conspiracy and you can see why.

The coincidence of Sunderland's Wes Brown scoring in his own net in last season's fixture here – the only goal of the game – and John O'Shea gifting his old team the opener yesterday was a wretched one. But it is a measure of Ferguson's eye for a dispensable player, rather than a fix. O'Shea, a one-time United defender-come-utility man, was sold because Phil Jones, the new United defender-come-utility man, seemed a better prospect. Jones's performance, in his first Premier League start of the season, bore out that judgement yesterday, demonstrating that if he can shake off the injuries which have curtailed him he can be a seriously dangerous player. Not something you could ever call O'Shea.

The Sunderland captain was a danger only to the defence which he anchored. His clearance, straight out for Robin van Persie to seize on, score and take United ahead, was something he will care to forget.

And games are also won or lost on a defender's failure to react, like O'Shea's, when Van Persie bisected Titus Bramble and Carlos Cuellar and crossed low for Wayne Rooney to tap in for 3-0. This was not defending of a Premier League quality. "They didn't really need any help from us which they did get," Sunderland manager Martin O'Neill said. "The goals we conceded were from our viewpoint not too clever. A difficult afternoon became more difficult."

O'Neill's squad is so pitifully small that he can't afford slip-ups. Only if everyone plays their part may Sunderland hope to take something, because you can forget all thoughts of a capacity to generate those surges of power which can make United so dangerous. This is part of O'Neill's inheritance from Steve Bruce, who hired players so relentlessly that his successor felt the need to end the churn and buy only three, with one loanee, this summer.

"You only have to look at the back of the programme to see we don't have any numerical strength," O'Neill reflected – and he was right. The comparative size of the squad lists was eye-watering. Though Sunderland had developed a reputation as aspirants in the Ellis Short era, they are truly in survival mode now. Yesterday was more make-do-and-mend than ever. The manager's only two functioning full-backs were injured and the man who has been standing in for them, Craig Gardner, had to be moved to midfield in the hope of generating something – anything – by way of forward momentum.

These were the extenuating circumstances. The outcome was a midfield so carved up in the first half hour that United could play arguably their most lavish football of the season. Adam Johnson, who didn't seem fully fit, looked like one of the Premier League's best in his better moments at Manchester City but here he vanished into the Manchester gloom, visible only when he was substituted.

The positive came in the way things perked up as Sunderland's afternoon wound towards its inevitable conclusion. They lasted the course and showed some vim, principally through substitutes Fraizer Campbell, who scored, and Connor Wickham. "We have to cope. I think we would have to be seriously looking to strengthen our side," O'Neill reflected. Theirs is an unsparing Christmas landscape, though: a relegation scrap with Southampton, followed by Manchester City and Tottenham. O'Neill's United old boys aren't used to this terrain. They need to acclimatise fast.