Most likely Porto will use a defensive strategy and target a draw at the Emirates, Arsenal will have difficulty beating Porto even though the goal margin is only 1-0. On paper Arsenal chances were very good, but when they dominated the match and created chances, no one could convert them into goals. Porto would really benefit if Arsenal still played with the same style, they also wanted to qualify for the quarter finals and Arsenal failed to anticipate their style of play.
Full defensive is very good tactical for FC Porto on second leg match against Arsenal, get capital winning over one goal and draw result on second leg match more enough for FC Porto qualifying to quarter final although Arsenal's advantage with playing in their home. I think will make frustrated with the opponent team when FC Porto make full defensive strategies on second leg match.
I think FC Porto can take advantage with counter attack with Arsenal will play more offensive make space with their defense position, be careful for Mikel Arteta if Porto will play more defensive and Arsenal payer get frustrated how difficult scoring goals make their defense players will leave their position.
Porto was just lucky with their win against Arsenal because the gunners dominated the match unfortunately couldn't capitalize on their dominance of the game by being wasteful in front of goal probably due to inexperience of their players, however I don't think Porto can defend their lone goal advantage at the Emirates it's going to be a different ball game because Arsenal would launch massive attack to win the return match knowing that failure to win means they are out of this season UCL, of course Porto would deploy a defensive tactics because of the attacking prowess of the gunners and utilize or adopt a counter attack