Porto vs Arsenal 1-0. Arsenal as a whole dominated the game but Porto's very strong defense made it difficult for Arsenal to score goals.
And Porto's 1 goal in the remaining extra time scored by Galeno in the 90+4 minute was a painful goal for Arsenal.
Arsenal lost the match in injury time but they will return to their home stadium to host Porto. It will be their foundation to beat Porto but they must admit that they played worse than Porto in a first match. Even Porto won with a late goal, they deserved it because Porto created more dangerous chances in the match than Arsenal.
Galeno scored a fantastic goal that helped Porto to have a difficult winning but it does not mean Porto did not deserve this winning.
The chance for Napoli to win in the second leg is very small. Although that doesn't mean they don't have a chance, it's just that the chance is very small.
They hosted Barcelona in Naples but did not play better than the guest and they will have to play at Nou Camp in a second leg without any advantage in result. I agree that Napoli does not have big chance to win against Barcelona in Spain but they actually can fight and achieve it. Weeks ago, Girona won over Barcelona at Nou Camp and I am sure Napoli are not weaker than Girona.