After securing a 2-1 away win at the Estadio do Dragao, it seemed likely that City would progress to the next round.
City's home record in European competition is imperious, having not lost since their 2008 clash with FC Midtjylland—a run stretching 16 matches.
But not many people predicted the demolition job that came at Etihad Stadium on Wednesday night.
The resounding 4-0 win against Porto has set up a tie with another Portuguese club, Sporting Lisbon.
Here are five things we learned from their Europa League triumph.