Arsenal recovered from a goal down to beat FC Cologne 3-1 after crowd disturbances in London, while AC Milanโs new signing Andre Silva scored a hat-trick in a rousing 5-1 win at Austria Vienna as the Europa League group stage got underway on Thursday.
Fellow Serie A sides Atalanta and Lazio also won while Portugalโs Vitoria Guimaraes began their match against Salzburg with not a single European player in the team.
Arsenalโs Group H match was delayed by an hour as about 20,000 Cologne supporters fans descended on The Emirates, most without tickets, before kick off as their team returned to European competition for the first time in 25 years.
The reports added that the number of away fans around the stadium was preventing home supporters getting in, although the Arsenal fans were eventually able to enter the stadium.
The Metropolitan Police said extra officers had been sent to the stadium after scuffles broke out before kick-off.
A police statement said: โOfficers are dealing with disorder at the Emirates Stadium where fans have gathered for the Arsenal vs FC Koln match. A policing plan is in place for the game. Additional officers have been deployed.โ
The police later said four people had been arrested โon suspicion of public order offencesโ.
Asked if the number of Cologne fans at the match was a surprise, Arsenal manager Arsene Wenger told reporters: โThey were very clever. I donโt know how they managed to infiltrate our fans and get everywhere but they did that very well.โ
โWere the problems created by people who had no tickets? I donโt know. But certainly they (Cologne) had more people here than tickets so that was certainly the cause,โ he said at the post-match news conference.
โIโve followed German football for a long time and I thought Cologne had not played in Europe for 25 years. On the first night they go out (to play), they spoil their night. I couldnโt understand that.โ
There were also scuffles between fans and when the action finally started, Arsenal fell behind to a stunning long-range strike from Jhon Cordoba before second-half goals from Sead Kolasinac, Alexis Sanchez and Hector Bellerin rescued the win.