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
How could that be luck? Porto achieved it with great difficulty and even until the last minute they didn't give up. Arsenal really deserved to lose because they couldn't produce results equivalent to what they performed in the English Premier League and once they lost they had to regret it because it was in a bigger competition. I still believe that Porto will do the same thing at home to Arsenal and if Porto succeeds in widening the aggregate then Arsenal will be eliminated in the Champions League.