Roberto Mancini insisted on taking the blame for the Blues' exit from the Europa League - and claimed he had underestimated Sporting in last week's crucial first leg.
City's 1-0 defeat in Lisbon came back to haunt the manager as his players conjured an heroic comeback for a 3-2 second-leg victory that saw Sporting squeeze through on away goals.
City trailed 3-0 on aggregate at half time but almost stole a famous victory when Joe Hart joined the attack for a last-ditch corner and saw his header tipped around a post.
Mancini said: "I am proud of the performance but disappointed for the two games. In the first game we didn't play well, today in the first half we didn't play.
It's my fault as manager. I probably made a mistake. The players did everything and I'm proud of them
"We probably didn't prepare well for the game. When I lose a game I think why? I think because I made a mistake. The manager is the person who prepares for the game and I must have made mistakes."
City had toppled Porto 6-1 in the previous round, and Mancini admitted: "I probably made mistakes in the first game. Probably we thought that after Porto, Sporting was maybe easier.
"But in football it's never easy. Today we left them a lot of space in the first half but in the second half we did a fantastic 45 minutes.
"I'm sorry for the supporters and I'm disappointed with myself, not the players, that in the end we lost."
But the Blues boss promises a battle royal for the Premier League title with Champions League quarter-finalists Chelsea next up at the Etihad next Wednesday.
He said: "We have only one problem, four important players injured. That's not good. But if we have the same spirit as in the second half we can win the next game against Chelsea.
"We are in second position one point behind, but I am very confident for the Premier League.
"Now it will be a good fight until the end of the season. We have only the Premier League and we can put all our strength into this. I think it will be good."