City were beaten 1-0 for the third successive season at the Stadium of Light, and the City boss said his men had only themselves to blame after former City player Adam Johnson hit the winner.
Mancini said: "We deserved to win. We had chances, but didn't score.
"This is our problem. We don't score enough goals to win the game.
"We are too soft in attack, too soft when we have chances, too soft when we shoot, sometimes we don't shoot, we want to have one touch more. This is not good."
Sunderland defended resolutely to ensure Johnson's contribution was decisive, but Mancini was less than gracious in his assessment of the game. He said: "Sunderland are lucky against us at home. You can't create every time 15, 20 chances like this year, last year, two years ago and lose."
However, Black Cats boss Martin O'Neill was not interested in Mancini's view. He said: "I have seen it with other managers. I just thought we were terrific."
Meanwhile, a Gareth Bale hat-trick helped Spurs romp to a 4-0 win over hapless Aston Villa.
And Liverpool's inconsistent season continued as they crashed 3-1 away to Stoke.
lNottingham Forest last night fired manager Sean O'Driscoll after beating Leeds 4-2 at home.