Olivier Giroud netted a hat trick to help Arsenal seal their passage to the last 16 of the Champions League, while Chelsea eased the pressure on Jose Mourinho to also advance.
Needing a win over Olympiacos away from home to qualify for the next stage of the UCL, Arsenal produced an emphatic 3-0 victory.
Giroud opened the scoring in the 29th minute, with a headed goal from an Aaron Ramsey cross.
The Frenchman scored again four minutes into the second half, before completing his hat trick in the 67th minute through a penalty.
Chelsea beat Porto 2-0 at Stamford Bridge to advance to the knockout stage and finish on top of Group G.
Porto's Ivan Marcano gave the hosts the lead through an own goal in the 12th minute.
William then doubled the lead in the 52nd minute give Chelsea fans a much needed win.
Match day six results:
Bayer Leverkusen 1- 1 Barcelona
Roma 0 - 0 BATE Borisov
Dinamo Zagreb 0 -2 Bayern Munich
Olympiacos 0 -3 Arsenal
Chelsea 2 - 0 Porto
Dynamo Kyiv 1 - 0 Maccabi Tel Aviv
Gent 2 - 1 Zenit St. Petersburg
Valencia 0 -2 Lyon