I missed out on the game but this was a crucial game, though I settled for highlights, Arsenal dominated the game fulltime but got unlucky when it comes to goals scoring.
You could also say they got a bit lucky since Porto failed to score more because they had more threatening chances. If their player quality is a bit better and they have more composure, I believe Arsenal can be 1-0 down earlier. That's just football, if you fail to score or create any chances then it means nothing, even if you have 70% possession. Kind of weird Arsenal suddenly failed to score after they battered teams in the PL.
Basically, regardless of the fact that Arsenal looks like a big name in football, Porto have more champions experience more than them because i have already stated it earlier before the match that despite the fact that Arsenal have been in a very good form in their domestic league that FC Porto have kept a record in champions league that Arsenal is yet to achieve and considering the fact Porto was playing at home made them very familiar with their play nature that's why it looked like all the efforts Arsenal were making was all in vain because normally, Arsenal dominated the game but their inability to make good attempts towards their opponents goal post made them felt very weak and tired thereby making FC Porto easy to take advantage of their weaknesses and were able to score Arsenal at the die minutes.
Arsenal needs to perform more better when FC Porto comes to the Emirate stadium otherwise Arsenal may find it so difficult just like they did in this 1:0 defeat they suffered to FC Porto so the duty of the coach now is to identify the areas that didn't work out in this first leg and probably change formation and make sure he makes the right features for their returning leg.