Napoli's decline in performance was completely sudden. They were consistently performing well. But suddenly Napoli conceded a 4-0 defeat against Milan in Serie A. This was a completely unexpected result. And in several matches after that, we saw erratic performances from Napoli. Napoli's performance against AC Milan was also poor in the Champions League match as well. And so Napoli failed to qualify for the semi-finals.
Both Inter Milan and AC Milan seem equally likely to win. The performances of these two teams have been erratic in Serie A this season as well. So there is no way to say for sure which team will qualify for the finals.
To be honest we expect Napoli to qualify for the semi-finals and can get rid of Ac Milan in the two quarter-final matches yesterday. Maybe we are more assuming because in Ac Milan is much more experienced in the League and gives wider chances to win yesterday, now Inter and Ac Milan meet again the two are tough Rivals, we will see who deserves to go to the next round.
Though I've not really been following the match of this two teams like back to back, but from the few matches I've watch the both team play respectively, I agree with you, AC Milan and inter Milan are two great team that are really good at what they do, but then, if this two teams are meeting, I will give the victory to AC Milan, I am not going to go into details as to why I think AC Milan will win, but let this just be as a prediction from me, inter Milan is great, but AC Milan is better based on my observations.