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.
FC Porto escaping with a lone goal in their home is impressive, kudos to them but I don't think they can repeat that when they visit Arsenal at Emirate in second leg.
Arsenal is stronger at home
To be honest, Porto's recent victory over Arsenal was largely due to luck; Arsenal's performance flagged as the game was about to end, Otherwise I doubt they could have scored in that match, as Arsenal played with great intensity in both the first and second halves. Everyone had a hard time seeing a goal because they both thought the game was really challenging.
However, given how well Porto has played Arsenal at home, I don't think they can duplicate that performance in the second leg. That being said, even though Arsenal is formidable at home, Porto will undoubtedly find the match extremely challenging.