The Argentine coach was delighted with the way his side fought back after falling behind at the Estadio do Dragao, saying the result is crucial to their chances of progressing
The Liga outfit fell 1-0 behind before the break following Jackson Martinez's goal, but strikes from Diego Godin and Arda Turan eventually helped them to the full three points, much to the delight of Simeone.
"There is happiness at achieving a very important result. It's incredible the reaction we produced. Everyone put in a great performance," the 43-year-old told reporters.
"We are very happy – we did a great job. It was a fantastic response to what was an adverse situation.
"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."
Atletico sit atop of Group G with six points from two games, three points ahead of second-placed Porto.