City won the first-leg of the tie 9-0.
“I want to give big congratulations to Burton for what they have done, they have beaten teams from the Premier League and Championship and deserved to be here," said Guardiola.
“The difference in Premier League teams is the rhythm, when you have high intensity. The physicality is higher and we scored quickly.
“It was important to try take advantage, we didn't expect to score as many but it's great. It means a lot for us.
“We spoke about that (being ruthless) at half-time - to be simple. To score is best way to respect the competition and the opponents."