A brace from Ricardo Quaresma in the opening 10 minutes set up Porto's surprise 3-1 victory on Wednesday.
Thiago Alcantara pulled a goal back for the 2013 European champions, before Jackson Martinez's second-half effort put the Primeira Liga giants in control of the tie.
"We were not surprised by Porto's start to the game. I knew we were going to face a very good team, we knew they had a good attack," Guardiola said.
"The quality of this game was at the highest level, we are lucky to be in this phase of the competition. Jackson Martínez is a top player. Casemiro and [Hector] Herrera played very well.
"In the Champions League you have to be practically perfect to win a match. It did not go well but we have six days to prepare [for the second leg]."
Hot favourites to progress to the semi-finals prior to Wednesday's clash, Bayern need a turnaround when they host the second leg on Tuesday.
Guardiola felt the away goal from Thiago was crucial for his side.
"This was a typical UEFA Champions League game. After 10 minutes we were already 2-0 down which was obviously not good for us," he added.
"We are down but we have six days to prepare for the next match – we will keep training and will try to play better in the second leg.
"Of course Thiago's goal is important but it is not decisive."
