Athens: Olivier Giroud was Arsenal`s hero as the Gunners and Chelsea succeeded on Wednesday where Manchester United failed a day earlier to advance to the draw for the last 16 of the Champions League.
The London clubs celebrated on the final night of group stage action as Roma, Dynamo Kiev and the Belgian underdogs Gent also secured their places in the knockout phase.
Arsenal had needed to overturn a 3-2 defeat at home to Olympiakos earlier in the season when they faced the Greek champions away in a Group F showdown.
Arsene Wenger`s side had lost in Piraeus on three separate occasions in recent seasons but France striker Giroud gave them a first-half lead and crucially doubled their advantage shortly after the restart following superb play by Joel Campbell.
Giroud then netted a penalty in the 69th minute to seal Arsenal`s place in the last 16 for the 16th season in a row, although finishing second in their group exposes them to the possibility of being drawn against Real Madrid or Barcelona in the next round.
Group winners Bayern Munich finished with a 2-0 victory at Dinamo Zagreb thanks to a second-half Robert Lewandowski brace as Thomas Mueller missed a late penalty and coach Pep Guardiola claimed his 100th win in charge.
"I told you before that it would be the greatest escape," Wenger told BT Sport, referring to successive defeats to Dinamo and Olympiakos to start the group that had put the Gunners in a perilous position.
"Nine times out of 10 you are out (after such a poor start). We needed something special to come back like we did and tonight we needed a complete team performance."
Enduring a difficult season domestically, Chelsea progressed to the last 16 as Group G winners with a 2-0 win at home to Jose Mourinho`s old side Porto as Ivan Marcano`s early own goal put them ahead and Willian scored in the second half.
"The players were really committed to get a result, as much for their pride. They didn`t want to go to the Europa League," Mourinho said, as his team avoided the fate of United, forced to settle for the consolation of dropping into the secondary continental competition after defeat at Wolfsburg on Tuesday.Porto started the day on top of the group but finished by tumbling into the Europa League themselves after being overtaken by Dynamo Kiev as the Ukrainian champions beat Maccabi Tel Aviv 1-0 through a Denys Garmash goal to reach the last 16 for the first time since 1999/2000.
Elsewhere, Roma advanced as runners-up in Group E despite a dreary 0-0 draw at home to BATE Borisov in the Italian capital.
That was because Bayer Leverkusen could only draw 1-1 at home to group winners and defending European champions Barcelona in Germany, unable to find the winner they needed after the in-form Javier Hernandez cancelled out Lionel Messi`s opener.
Leverkusen go into the Europa League, and that is the consolation that Valencia have to settle for after they were beaten 2-0 at home by Lyon in Group H in former England defender Gary Neville`s first match as head coach of the Spaniards.
Maxwel Cornet and Alexandre Lacazette scored to give already eliminated Lyon a consolation win, although it was all academic for Valencia anyway as Gent`s 2-1 victory at home to Zenit St Petersburg took them through.
"It`s disappointing. Obviously we wanted to win the game, but we have no complaints," said Neville.
Laurent Depoitre and Danijel Milicevic netted for Gent either side of a strike by the prolific Artem Dzyuba as the Buffalos became the first Belgian club to reach the knockout stages of the Champions League.
The draw for the last 16 will take place at UEFA`s headquarters in Switzerland on Monday.