Despite hammering Plzen 5-0 on October 23, the European champions could only squeeze past their opponents by just the one goal this time round.
"Some fans must have thought that after winning 5-0 at home to Viktoria it would be easy for us, but in the Champions League every game is tough," Guardiola is quoted as saying on UEFA.com.
"This match was no exception.Viktoria have a very good team, but we are the only side so far that have managed to get maximum points from all four of our games. This shows our strength.
"We knew it would not be easy and this is also the case in the Bundesliga. When you play a second time against the same opponents it is always a different game. After losing by five goals, they learned their lesson."
Bayern booked their place in the knockout stages with Tuesday's victory.