Jamie Vardy scored a hat-trick as Leicester scored three times in the first 20 minutes and then went 4-0 up, before late goals from Aleksandar Kolarov and Nolito added an air of respectability to the scoreline.
City had previously fallen to a 3-1 home defeat by Chelsea, who can put seven points between themselves and Guardiola’s side if they win at home to West Bromwich Albion on Sunday.
“Four minutes, 2-0, is not easy,” Guardiola told BT Sport.
“England is so good at one thing, the second balls. The counter-attack and the second balls. They (Leicester) are so tough on the counter-attack and defend so well.
“We tried until the end. Always in the game there are some good things. We tried, but it is difficult at that level after 2-0 and 3-0.
“They played long balls. We knew that. They win the ball, they were looking for our (defence) and they did well.”
Guardiola once again tinkered with his starting formation, aligning a back three and deploying right-back Pablo Zabaleta in midfield alongside Fernando and Ilkay Gundogan.
City have flitted between a back three and a back four since Guardiola succeeded Manuel Pellegrini as manager, but he said: “It is not about the system.”
It was City’s third defeat of the campaign and they have registered just one clean sheet in their last 17 outings.
Asked how long it would take for his methods to take effect, Guardiola told the BBC: “I don’t know. In the beginning it was quickly, now it will be a little bit longer.
“To change the mentality, to change what we want, maybe it will take a little more time.”
Would you like to place a soccer bet? Click here to get started in 3 easy steps.