Manchester United's dwindling hopes of lifting a trophy this season are dangling by a thread after they produced an abject display to lose 2-0 at Olympiakos Piraeus in a Champions League last-16 first leg on Tuesday.
Alejandro Dominguez opened the scoring with a clever first-half flick and Arsenal loanee Joel Campbell added a sublime second goal to leave United facing a huge task to overturn the deficit in the return match at Old Trafford on March 19.
"That's the worst we've played in Europe. We didn't deserve to get anything," manager David Moyes told reporters. "I'm surprised, I didn't see that level of performance coming.
"I take responsibility, we have to play better. The players are hurting."
Defeat at the Georgios Karaiskakis Stadium represented yet another body blow in an inauspicious campaign for last season's English Premier League title winners.
United are out of the FA Cup and the League Cup and trail Premier League leaders Chelsea by 15 points with 11 games left to play.
Moyes's men looked sluggish and disjointed against an inexperienced Olympiakos side who are bidding to reach the quarter-finals for only the second time in their history.
It was the first time the Greeks had beaten United in five attempts.
"To beat a great side like United, the way we did, is something very special and I can't hide the joy and pride I feel for my players," said Olympiakos coach Michel.
"We picked the best moment to show Greek football is alive and kicking," added the former Spain and Real Madrid striker.
Moyes opted to start with two wingers, Antonio Valencia and Ashley Young, but neither made an impact in a first half in which runaway the Greek league leaders displayed real energy and hunger.
After a cautious opening from both sides amid ear-splitting noise from an enthusiastic home crowd, the first chance fell to Olympiakos as Dominguez burst through the middle on a solo run only to be denied by a last-ditch tackle from Nemanja Vidic.
Midfielder Tom Cleverley registered United's only effort of note in the first half with a 17th-minute half-volley that sailed high over the bar.
Strike pair Wayne Rooney and Robin van Persie were peripheral figures for the visitors as pot shots on goal from Giannis Maniatis and Hernan Perez lifted the home supporters.
Olympiakos, wearing bright red and white jerseys, red shorts and socks, broke the deadlock seven minutes before halftime with a smart piece of improvisation from Argentine forward Dominguez.
Patrice Evra's half-hearted clearance from a corner landed at the feet of Maniatis 25 metres out and his tame, low shot was expertly diverted past keeper David De Gea by Dominguez's flick.
United, the European champions in 1968, 1999 and 2008, were punished again for poor defending 10 minutes into the second half.
Campbell, who is likely to feature for Costa Rica against Group D rivals England at the World Cup in Brazil in June, did the damage.
He picked up possession 25 metres out, jinked past midfielder Michael Carrick and sent a curling left-foot shot round defender Rio Ferdinand and into the bottom corner of the net.
Moyes sent on Danny Welbeck and Shinji Kagawa for Valencia and Cleverley but it was more a change in attitude than personnel that was required from United.
Dutch striker Van Persie summed up his team's night with five minutes to go. He received the ball 12 metres out and turned inside a defender before blazing a right-foot shot way over the bar.
"It is a great moment for us and we will enjoy it but we must look ahead to the second leg. Whoever thinks 2-0 is enough to qualify is mistaken," said Michel.
"We expect a different United at Old Trafford. We have huge respect for them so we have to keep working if we want to write another piece of history."
Olympiakos Piraeus made it fifth time lucky on Tuesday, beating an abject Manchester United team 2-0 in their Champions League last-16 first leg.
Alejandro Dominguez opened the scoring with a clever first-half flick and Arsenal loanee Joel Campbell added a sublime second to leave United facing a huge task to overturn the deficit in the return match at Old Trafford next month.
Defeat represented another body blow in an inconsistent season for David Moyes's men.
The Champions League is United's last chance of a trophy and they looked disjointed and sluggish against an inexperienced Olympiakos side who are bidding to reach the quarter-finals for only the second time in their history.
It was the first time the Greeks had beaten United in five attempts.
Rodriguez opened the scoring in the 38th minute when his clever flick just inside the box deflected a long-range shot past keeper David De Gea.
Campbell put the game beyond United 10 minutes into the second half with a brilliant curling left-foot effort from 20 metres.
Robin van Persie had United's best chance in the closing stages but he ballooned the ball way over the bar.
Man United 0 Olympiakos 2 (Dominguez 38" Campbell 54")
An erratic and lacklustre Manchester United were beaten comprehensively by Olympiakos in the Champions League match at the Karaiskakis Stadium, Athens, on Tuesday night.
A goal by Alejandro Dominguez (38th) and Joel Campbell (54th) made Olympiakos the first team to win a home match of the last 16 first leg.
The win was sweet revenge for the Greek champions who had lost their previous four outings to the Premier League side.
David Moyes will have to draw on all his experience in the return leg which is in three weeks' time as his boys were totally off colour against a Greek side who are lions in their own den having won 24 of their 26 games.
Robin van Persie missed an open goal towards the fag end but that was all the Old Trafford boys had to show for their poor display.
90" United make a desperate last-ditch attempt to score with Kagawa and Evra working in tandem but Evra's shot is blocked by a defender.
89" YELLOW! Rio Ferdinand is booked for a rough tackle.
88" Welbeck and Persie make inroads but Persie's sliding shot lacks power as is gloved by Roberto.
85" The picture is not looking good for United fans here with only five minutes to go for the long whistle.
84" United have been pressing in a bid to pull one back but they lack the finishing touch.
81" What an opportunity Van Persie let go, one of few that he got. With only Roberto at his mercy, Persie controls the ball with his left foot and moving it to his right, shoots over from close.
80" United look totally disoriented with even Van Persie and Rooney unable to come up with a single notworthy move.
75" With 15 minutes left Olympiakos coach Michel takes a gamble removing both his goalscorers. But United are so uninspiring and unimpressive that even if Olympiakos play with 10 men they will win.
75" Dominguez gets a round of applause as he is substituted.
72" United are running out of ideas and time to pull at least one goal back.
67" Goal-scorer Campbell makes way for David Fuster
65" Olaitan goes close with a left footer.
64" Giannis Maniatis has a crack at the United goal but is unhappy with his shot which goes wide.
60" Moyes makes two substitutions bringing in Welbeck and Kagawa. Valencia and Cleverley make way for them
54" GOAL! Another defensive lapse and Joel Campbell makes United pay the price with a clinical left footer from just outside the box which beat the outstretched hands of De Gea.
49" Moyes will need to make some changes as United look out of sorts here, their passing is atrocious and they just seem to be surrendering the ball.
47" Olympiakos mean business as Perez makes a dazzling run through the defence but his weak shot is collected easily by De Gea.
Manchester United paid the price for being defensive in the first half as they trail Olympiakos by a solitary goal in the Champions League last 16 first-leg match at the Karaiskakis Stadium, Athens, on Tuesday night.
Alejandro Dominguez scored in the 38th minute after his shot, which lacked power, luckily deflected off a defender and caught goalkeeper De Gea on the wrong foot as the ball entered an empty net.
United will have to come up with something extraordinary in the second session especially after a lacklustre show so far.
The crowd is not making it any easy for Moyes' side with their booing and jeering with every touch of the ball by the United players.
Brace yourselves for a better second half.
Man United 0 Olympiakos 1 (Alejandro Dominguez 38")
40" Rooney free-kick is headed for a corner before Van Persie can get to the ball.
38" GOAL! Dominguez gets lucky as his not so powerful shot deflects off a defender catching De Gea off his balance.
32" Less than 15 minutes to go for the half time whistle and neither teams has really come very close to scoring.
28" Interesting run by Joel Campbell as he goes unchecked from the halfway mark into the United box until he is foiled.
27" United were expected to dominate but Olympiakos have more ball possession.
25" Hernan Perez tries a long range shot which just goes wide of De Gea's goal.
22" Rooney's corner kick is punched clear by Roberto.
19" Valencia and Smalling engage in some good passing but Valencia's cross is way off the mark.
16" United earn their first corner and Cleverley has a shy at the goal but shoots over.
15'' United try to slow the pace by keeping possession of the ball in their own half.
10'' First ten minutes and Olympiakos with a vociferous crowd behind them push Utd on the back foot.
8'' Great tackle from Vidic as he blocks Dominguez from scoring from six yards.
5'' Some sloppy defending by United but Olympiakos fail to capitalise.
4'' A hostile crowd start to jeer the United players every time they touch the ball
2'' YELLOW CARD! Early booking for Patrice Evra as he handles the ball deliberately.
1'' Olympiakos get the match underway.
Wayne Rooney will be making his 77th Champions League appearance with 29 goals to his credit.
If Olympiakos win they could become the first team to win at home of all the matches played so far in the last 16.
There's no Adnan Januzaj in the United squad and Ryan Giggs is on the bench.
United XI: De Gea; Smalling, Ferdinand, Vidic, Evra; Valencia, Carrick, Cleverley, Young; Rooney, Robin van Persie.
Subs: Lindegaard, Büttner, Fellaini, Giggs, Kagawa, Hernandez, Welbeck.
Manchester United are unbeaten in the Champions League so far, winning four and drawing two of their six games this season.
Olympiakos won their last three games against English teams.
Ryan Giggs is only three games short of equalling Raul’s record of 142 appearances in the Champions League.
In United's four meetings with the Greek side, stretching over more than a decade, Giggs has started each game and has been on the winning side on every occasion.
Both teams likely to play a 4-2-3-1 formation.
Manchester United have never lost to Olympiakos in four previous outings in the Champions League which makes them favourites to win Tuesday's last 16 first-leg clash at the Karaiskakis Stadium, Athens.
However, times have changed since as the English side under David Moyes seem to be struggling to find their feet, and goals, as they totter in sixth position in the Premier League whereas their opponents are 20 points ahead of their nearest rivals in the Greek Super League.
Although it is considered one of the weakest leagues in Europe, one cannot rule out Olympiakos' chances especially after seeing their recent record where they have won 24 of their 26 league matches and are yet to lose one.
In contrast, United have lost 10 times this season in all competitions.
Adding to their woes will be the absence of defenders Phil Jones (hip) and Jonny Evans (calf) who did not travel with the team.
Nani is also sidelined with a hamstring injury, while record signing Juan Mata is cup-tied after playing in the competition with Chelsea.
This leaves Moyes banking fully on Wayne Rooney and Robin van Persie.
Wayne Rooney celebrated his new deal with the club when he helped them to a 2-0 win over Crystal Palace on Saturday.
The England international pledged his long-term future to the Old Trafford club by agreeing a new five-and-a-half-year deal on Friday.
Danny Welbeck too is expected to add solidity to the attack.
Olympiakos will miss the services of their top scorer Javier Saviola who is out with a thigh problem.