This isn't the first abysmal Manchester United performance this season but it might be David Moyes' most desperate defeat considering how easily an unspectacular Olympiakos side exposed United's weaknesses. The Greek champions were superior defensively, more purposeful going forward, calmer in possession and highly energetic without the ball, pressing United consistently and forcing mistakes.

Olympiakos were impressively proactive without the ball, evident from the structure of their midfield, where the coach, Míchel, used Delvin N'Dinga as the sole holding midfielder rather than asking the captain, Giannis Maniatis, to sit alongside him to offer cover against Wayne Rooney. This meant Maniatis was free to push forward and join the more technical Alejandro Domínguez closing down Michael Carrick and Tom Cleverley. For long spells the home side's pressing was excellent, winning the ball high up the pitch and refusing to let United settle.

Another crucial part of the home side's performance was the direct dribbling of the wonderful Domínguez, who started from a centre-left midfield role. The Argentinian was the game's best player and it's rare to see a central midfielder carry the ball forward so directly. That highlighted United's complete lack of a genuine tackler in midfield, someone who can stop opponents with force when required.

Domínguez seemed to surprise Carrick and Cleverley with his immediacy and determination in possession – arguably the only comparable Premier League player is Tottenham's Mousa Dembélé, who, interestingly, has consistently played well against United. Domínguez's mazy dribble exposed United's poor defending in the early stages, with only a superb Nemanja Vidic saving tackle delaying him from opening the scoring. Centre-forward Michael Olaitan also deserves great credit. He is unspectacular technically and offered little goal threat, but his sheer energy up front completely exposed Vidic and Rio Ferdinand's lack of mobility. The majority of his work involved basic, tireless, off-the-ball running – but he encouraged his team-mates to press in midfield, and while United actually dominated possession throughout the game, it was rare for them to enjoy sustained spells of pressure inside the opposition half, at least until the final stages.

When United were attempting to attack down one flank, Olaitan was invariably towards that flank, preventing Moyes' side from switching play via the centre-backs. United's passing in deep positions was woeful and while various individuals were responsible for sloppy passes, Olympiakos deserve credit for forcing the mistakes. Ferdinand, in particular, produced one of the poorest performances of his Manchester United career and while the centre-back's declining pace means any positional errors have inevitably become more obvious, such lack of composure in possession is less forgivable.

Moyes did not offer a clear solution to United's problems – there was no obvious game-changer to help bypass Olympiakos' press. The introduction of Danny Welbeck helped slightly, as he offered pace from the left flank, but Shinji Kagawa was starved of service.

In fact, Míchel's defensive-minded substitutions changed the game in United's favour. The Spanish coach removed Domínguez and the pacy right-winger Joel Campbell – the two goalscorers and two most obvious threats on the break. Simultaneously, he shifted Maniatis alongside N'Dinga and introduced Paulo Machado, another disciplined midfielder, and Olympiakos sat much deeper.

In the final 15 minutes United had their first real spell of pressure, even if genuine goalscoring chances were rare. Moyes will pray Olympiakos begin the second leg as cautiously as they finished the first.