Arsenal became the victim of Olympiacos’ first ever win in England following a 3-2 loss at the Emirates Stadium.
The Greeks took a first half lead when a corner to the edge of the box wasn’t picked up by the Gunners, and Felipe Pardo was on hand to strike the ball into the far hand corner.
However, this lead lasted all of two minutes, as Theo Walcott continued his fine scoring form to equalise.
With five minutes remaining before half time, Arsenal were punished from a corner yet again, as stand-in goalkeeper David Ospina fumbled the delivery over his own goal line.
Alexis Sanchez brought the hosts level again in the second half, but just 59 seconds later, Alfred Finnbogason stabbed home the Olympiacos winner.
Like their London rivals, Chelsea also slipped to defeat, as Jose Mourinho suffered a 2-1 loss at his old side FC Porto.
Midfielder Andre Andre pounced on Asmir Begovic’s parry to give the Dragoes the lead shortly before the interval, but a sublime Willian free-kick made sure it was level going in at the break.
Early in the second half, Porto captain Maicon headed a corner past Begovic at his near post to wrap up the points as Chelsea’s miserable start to the season goes on.
For Arsenal, their task of qualifying from Group F looks even more daunting. Their next two Champions League fixtures come against Bayern Munich, who ruthlessly disposed of Dinamo Zagreb with a 5-0 win at the Allianz Arena.
Douglas Costa and Mario Gotze both grabbed goals for the Bavarians, but Robert Lewandowski stole the show again with another hat-trick for the Bavarians to take his tally to 10 goals in a week.
Chelsea’s next opponents in Group G, Dynamo Kyiv, claimed their first Champions League victory in three years with a 2-0 triumph at Maccabi Tel-Aviv.
Former Everton target Andriy Yarmolenko gave the Ukrainians the lead early on and Moraes ensured Dynamo moved up to second in the group.
In Group E, Barcelona suffered a scare to their Champions League hopes, but managed to dig out a 2-1 victory over Bayer Leverkusen – Sergi Roberto and Luis Suarez’s late goals were enough to cancel out Kyriakos Papadopoulos’s early header.
One team that did suffer a shock defeat in group E were Roma, who were beaten 3-2 by BATE Borisov. The Belarusian minnows stunned Europe as Igor Stasevich netted once and Filip Mladenovic twice to put them 3-0 up after half an hour. Gervinho and Vasilis Torosidis pulled goals back for Rudi Garcia’s side, but they fall to fourth in the group.
Group H saw Zenit move three points clear at the top after a 2-1 win over Belgian champions Gent. Artem Dzyuba put Zenit ahead after 35 minutes, but Thomas Matton surprisingly levelled proceedings just before the hour mark – Oleg Shatov found Zenit’s winner 10 minutes after.
Elsewhere, a sole Sofiane Feghouli goal was enough to give Valencia all three points, as they ran out 1-0 winners in Lyon.
Player of the Night: Robert Lewandowski (Bayern Munich)
Team of the Night: Olympiacos
Goal of the Night: Luis Suarez (BARCELONA vs Bayer Leverkusen)