Joel Campbell Olympiakos Maniatis
Olympiakos forward Joel Campbell celebrates with teammates after scoring against Manchester United in the Champions League, 25 February. Reuters

Manchester United used to be a team that had this unerring habit of winning - be it when they have played at their peak, or when they have been downright shoddy. However, following Sir Alex Ferguson's retirement, all those obvious player failings, which were shut and locked inside a room deep down a dark hole during Ferguson's reign, have come out into the open and laid siege on the club this season.

In yet another what-on-earth-is-going-on-with-this-side performance, Manchester United went down 2-0 to Olympiakos, who just took full advantage of a side bereft of confidence, and apparently quality, in the first leg of their Champions League last 16 game.

A packed Georgios Karaiskakis stadium saw their home side pick the former European champions and current English Premier League title holders apart, with the two goals coming via Alejandro Dominguez and Arsenal's on-loan forward Joel Campbell -- an absolute peach.

United started the match nervously with Rio Ferdinand and Chris Smalling making early mistakes and only a bit of last-ditch defending preventing Olympiakos from taking the lead.

The game was not exactly a now-this-is-worth-my-money encounter, but Olympiakos were the better side and took the lead in the 38th minute, with Dominguez diverting Giannis Maniatis' speculative effort into the back of the net.

United needed to come out and show a bit more fight and quality in the second 45, but it was Olympiakos that extended their lead nine minutes into the half, with Campbell scoring a brilliant solo goal.

The Arsenal man moved past a Michael Carrick, before curling a wonderful effort around Ferdinand and past the despairing dive of David De Gea.

Robin Van Persie had a great opportunity to at least grab what would have been a vital away goal for his side late on, but the Dutchman fired high from 12 yards out.

United now have it all to do to stay alive in the Champions League -- the only possible silverware remaining this season, and their best chance at the moment of qualifying for next season's Champions League.

In the other game of the day, last season's runners-up Borussia Dortmund eased to a 4-2 victory over Zenit St. Petersburg.

Questions were raised over Dortmund's form after a poor run in the Bundesliga, but Jurgen Klopp's men eased those worries by hitting top gear right from the off with Marco Reus and Henrikh Mkhitaryan scoring in the first five minutes of the match.

Robert Lewandowski then made it 3-1 just past the hour mark after Oleg Shatov had got one back for the home side a few minutes earlier, before Hulk, via the penalty spot, made it interesting.

However, Lewandowski put the first leg beyond doubt by completing his brace on 71 minutes to give Dortmund a healthy lead going into the second leg at the Westfallenstadion.