If Olympiakos are supposed to be the weakest team left in the Champions League then one wonders how United would have fared against one of the stronger outfits.
They came into the last-16 tie amid bold talk of overcoming poor domestic form and putting a silver lining on their season by winning Europe’s elite club competition.
But those ambitions were cruelly exposed in the intimidating atmosphere of the Georgios Karaiskakis stadium.
Moyes is going to have to spark a marked improvement and United will need to summon up all their famous comeback skills in the second leg at Old Trafford in three weeks if they are to reach th last eight and keep hopes alive of winning the competition.
Goals either side of half-time from Alejandro Dominguez and Arsenal loanee Joel Campbell gave the Greek champions their first win in five attempts against United.
To compound a bad evening, Robin van Persie missed a great late chance to pull back an away goal which would have put an entirely different complexion on the tie.
The one big positive for United is that Olympiakos and other Greek clubs are notoriously bad travellers. And they will recall that Liverpool, having lost away 1-0 to Olympiakos, then fell one down at home before storming back to win 3-1 to scramble through their group before going on to win the competition.
But apart from a 4-0 win over Norwich in the Capital One Cup third round, United have not beaten any tream by three clear goals at Old Trafford this season.
And United’s powers of recovery are on the wane. They have now conceded the first goal in 16 games this season – lost 11 of them, drawn one and won only three of them.
They have also only recovered a 2-0 first leg deficit once in all their years in Europe – when Ron Atkinson’s side pulled off a famous Cup Winners’ Cup 3-0 home win over Barcelona in 1984 after losing 2-0 in the Nou Camp.
Moyes will be concerned how vulnerable his team looked all night and also – without the creative influence of the ineligible Juan Mata – how little they created going forward part from that late chance for Van Persie.
Moyes will come in for criticism for leaving Adnan Januzaj not only out of his starting line-up but also from his bench. The 18-year-old Januzaj may lack Champions League experience but he has the youthful talent and exuberance to make an impact as a substitute.
Januzaj was one of three changes from the team that secured a confidence-boosting Premier League win at Crystal Palace on Saturday. Tom Cleverley, Antonio Valencia and Ashley Young came in for Mata, Januzaj and Marouane Fellaini, who was on the bench.
Olympiakos were not expected to have much power up front having sold had sold striker Kostas Mitrogolu to Fulham while Argentine veteran Javier Saviola was ruled out by injury.
Considering the lack of competitiveness in the Greek League, Olympiakos had done well to pip Benfica for second place in their group behind Paris St Germain. And they caused United plenty of problems. Only a superb last-ditch tackle by skipper Nemanja Vidic prevented an early goal by Dominguez as he burst clean through and looked certain to score.
After a nervy first 15 minutes, United finally started to string their passes together and enjoy some sustained spells of possession. But when their first chance came from a partially cleared corner, Cleverley sliced his shot wide.
There was another scare for United when Hernan Perez cut in from the left wing, eluded Smalling’s challenge and fired a low shot into the side netting. United had just appeared to get a foothold in the game when they fell behind after 37 minutes to what a fortuitous effort at first glance but proved to be a great piece of improvisation from Argentinian Dominguez.
Patriced Evra’s clearance fell to Giannis Maniatis who shot from 25 yard into a crowd of players took a deflection off Dominguez and completely wrong-footed De Gea as it rolled into the opposite corner of the net.
If the first half had ended badly for United they found themselves in an even worse position early in the second half with Olympiakos increasing their lead after 55 minutes.
There did not look to much danger when Michael Olaitan played the ball to Campbell 25 yards form goal. United appeared to have enough players back but Campbell went through a flimsy challenge by Carrick to bend a superb left foot shot round Rio Ferdinand and past De Gea’ s despairing dive as it flew into the far corner of the net.
De Gea appeared to be late in reacting but his sight line may well have been hindered because the shot came round Ferdinand. It was a speculative strike but there was no doubting its quality.And it left United with an uphill battle not only on the night but also to retrieve the tie overall.
Moyes reacted by making two substitutions, sending on Danny Welbeck and Shinji Kagawa coming on for Antonio Valencia and Cleverley.
But the changes sparked no immediate improvement and it was Olympiakos who went close to a third when Olaitan sent a shot just wide It could have looked much different had Van Persie not blazed a great chance over the bar after taking Chris Smalling’s cross past Kostas Manolas.