City will face Arsenal at an empty Wembley in the last four next month after the Gunners struck in stoppage time to beat Sheffield United 2-1.
Chelsea were 1-0 victors at Leicester thanks to Ross Barkley's winner which set up a semi-final clash with Manchester United.
Kevin De Bruyne's penalty and a stunning strike from Raheem Sterling got City back to winning ways on Tyneside after a 2-1 defeat at Chelsea in midweek crowned Liverpool Premier League champions for the first time in 30 years.
"In the Premier League we are struggling to focus," admitted Guardiola. "Now the Cup and the Champions League it is a little bit different."
"We should score more but we played really well and created enough chances to score a lot of goals," said De Bruyne.