"We are very happy – we did a great job. It was a fantastic response to what was an adverse situation," Simeone told reporters at a press conference.
"The first 25 minutes were hard for us, Porto were very strong then. When we changed our way of playing in midfield from the 30th minute, the game also changed. We made key tactical switches which helped us as we looked to play into spaces and get closer to their penalty area.
"The lead-up to our second goal was something we had worked on. There is happiness at achieving a very important result. It's incredible the reaction we produced tonight. Everyone put in a great performance. The team must be congratulated. We will go on taking things game by game."
Atletico have also won all seven of their La Liga fixtures this season.