The Bundesliga champions returned to Munich trailing 3-1, but responded at home with a 6-1 win on Tuesday to reach the UEFA Champions League semi-finals.
In the days leading up to the clash, Guardiola knew Bayern would progress despite their struggles in the first leg.
"We've had problems creating chances and scoring goals in recent matches, but today we've scored six," he said.
"We had trouble controlling the game in the second half, partly because Porto changed their tactics. But they still had very few chances.
"Over the last few days I sensed we would do it.
"Obviously tactics and the line-up are important, but at the end of the day mental strength makes the difference at this level."
Robert Lewandowski netted a brace for Bayern as they struck five times in the opening 40 minutes at Allianz Arena.
Guardiola said he was unfazed by who his team faced in the last four.
"I don't care too much who our next opponents will be," he said.
"We will try our best whether it is Real, Barca, Atletico, Juventus or Monaco, that doesn't matter."
