Roberto Mancini accused Mario Balotelli of "throwing his quality out of the window" after the 3-2 derby defeat to Manchester United.
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But despite seeing his team slip six points behind their rivals and lose their 37-match unbeaten home league run come to an end, the Manchester City manager declared that they could still win both the his Premier League and the FA Cup.
"I am sure we can win the double this year," said Mancini, who added that he had been heartened by his team's comeback from 2-0 down before Robin van Persie's injury-time winner. "We showed we can win the title again this year. This season is a long one."
However, the manager said he believed Balotelli, a surprise selection to start, had let him down before he substituted the striker, who stormed off down the tunnel.
"When you have a player with the quality Mario has, you can't understand why he continues to throw his quality out of the window," Mancini added.
"It is incredible. In my life, I saw a player with fantastic quality who did nothing. I don't want Mario to finish like him. He can't continue to play like today. We wanted more from him. He has everything [but did not do enough]."
The City manager also blamed Samir Nasri, who deflected in Van Persie's last-ditch free-kick. City had three men in the wall but Mancini, referring to the Frenchman, said: "Two and a half."
Mancini was also annoyed that Carlos Tevez, who he had hoped would be a fourth man in the wall, had left it but could not get his message through to the Argentine amid the noise at the Etihad Stadium. "I called Carlos to return to the wall," he said.
The 48-year-old rued United's two first-half goals, scored after City had started the stronger, and said: "For 20 minutes they didn't touch the ball, and the first chance they got they scored a goal.
"We recovered very well and we dominated the second half. We wanted to win the game and we had chances. We have showed we are a really strong team. We didn't deserve to lose this game. We played very well."