Gabriel Jesus netted four times, while Kevin de Bruyne, Oleksandr Zinchenko, Phil Foden, Kyle Walker and Riyad Mahrez grabbed one goal each as well.
"We didn't expect anything less with the gulf between the two teams, we thought it could have been more", he said.
They can inflict further pain on Nigel Clough's side in the second leg at the Pirelli Stadium, on January 23.
That was also why Guardiola was quick to run on to the pitch to speak to the Burton players at the full-time whistle.
Despite the 9-0 scoreline, City's fans were keen for more goals as chants of "we want 10" rang around the ground before the final whistle.
"The result was good and of course we are already in the final but we have to play the second leg", said Guardiola.
"We've not gone into any detail with them because that will frighten the life out of them", admitted Clough.
Trump plans prime-time address, border visit as shutdown fight continues
House of Representatives, and passed legislation to reopen all closed government agencies but did not include wall funding. And Trump has threatened to drag on the shutdown for months or even years if he does not get funding for the border wall.
Malaysia's royal council meets after king's surprise resignation
Permatang Pauh MP Nurul Izzah Anwar thanked Sultan Muhammad V for giving a full pardon to her father, Datuk Seri Anwar Ibrahim. His abdication is a first for Malaysia since the country gained independence from the United Kingdom more than 60 years ago.
Trump walks out of meeting as White House confab devolves
There was no sign Trump was backing down from his demand for $5.7 billion for the border wall in exchange for ending the shutdown. Critics say the security risks are overblown and the administration is at least partly to blame for the humanitarian situation.
"I watched them play Liverpool and they were pretty frightening at times", he said.
The Gunners managed to qualify to the fourth round after they convincingly beat Blackpool over the weekend where Elneny was given his regular start by Unai Emery in cup competitions. "You can not be 'oh, it's Burton" and we did not - that is why I'm pleased.
"We are not a team that have a lot of titles in our museum so every chance to make a final you have to take".
"Do I wish we hadn't played?"
Ahead of the first leg of the tie on Wednesday night, Clough spoke to the media, and made comparisons between the respective draws against the Manchester clubs. "To score is best way to respect competition and the opponents".
Jesus continued his troubling act on the hapless visitors by completing his hat-trick with a ideal header from close range on 57 minutes.
"They got a massive squad of players that cost a fortune and earning a fortune, that's what you get in the Premier League so it's chalk and cheese".