The Premier League champions claimed a memorable 3-0 victory over their German counterparts at the Etihad Stadium on Tuesday in the first leg.
A stunning curling long range effort from Rodri in the first half was added to by second half goals from Bernardo Silva and Erling Haaland as City put one foot into the semi-finals.
But Guardiola knows the task at hand is far from over, having seen at first hand the mentality of the Bavarians during a three-year spell at the Allianz Arena as manager.
"Of course, when you are there you realise how good they are as a team, Bayern Munich," Guardiola told BT Sport.
"During 55, 60 minutes it was a tight, tight game and in a lot of moments they were better than us."
"We made some changes and our pressing was more effective," Guardiola added.
"With the ball we were better too, and I'm happy for the result, but I lived three years in Munich. I know the Bayern Munich mentality, I know the quality they have.
"It's a really, really good result, but we have still the second leg to play. The players know it. It's not necessary to tell them here in front of you, tomorrow, or before the game, how difficult they are. They know it. [Bayern] are a really good team, but we're going to take the mentality to play, to play, to play, and to try to win the game."
