Manuel Pellegrini admitted his team were far from their best after narrowly beating Sheffield Wednesday 2-1.
The champions trailed from the 15th-minute before finally leveling just past the hour-mark and then grabbing a winner in injury time to finally see off a stubborn and much-improved Owls side.
“I’m relieved because I don’t think we played very well today,” said Pellegrini.
“Apart from the last 20 minutes, we played very badly because we didn't press well, we didn't have good movement and we didn’t make any chances while Sheffield Wednesday had just one opportunity from which they scored.
“We tried to change things in the final half-hour and found another gear and with Yaya Toure, James Milner, Samir Nasri and David Silva all on the pitch, we began to find space and finally create chances
We have had many games in the past ten days so today we started with virtually the same side that beat Sheffield Wednesday in the Capital One Cup with only Martin Demichelis and Edin Dzeko missing and Yaya and Jovetic in their place
“Each game is different and we didn’t do as well this time, but as soon as we returned to our normal formation in midfield we looked much better and scored two goals.
“We didn’t expect it to be easy today and when you go behind to a side from the Championship, they make it hard for you and they played very well today.
“The FA Cup is a fantastic competition and there is one game a month from now until May and it is something we will be doing our best to win.”
Two-goal hero James Milner and Jesus Navas came in for special praise from the Blues’ boss who added: “I’ve stated a number of times this season that James is a very important player for us. He always gives us 100% in commitment and intensity so I’m very happy for him and very happy with his contribution.
“Navas works very hard for the team as well both in attack and defence and did so again today. Overall, we weren’t at our best and I am happy to be in the next round.”