The Italian coach was forced to replace Gareth Barry with Sergio Aguero after 35 minutes to try and get back into the game after the hosts dominated early proceedings, before Luke Moore headed the winner on 83 minutes.
The loss means that the Etihad Stadium outfit relinquish their lead at the top of the Premier League and fall to second place; Mancini feels his men did not deserve to be beaten.
“I think they played very well for the first 35 minutes, they were aggressive and had possession,” Mancini told Sky Sports.
“In the last 10 minutes of the first half and in the second half, we had control of the game.
“We had some chances where we should have scored but didn’t and we made a mistake for their goal.
“They had a lot of possession so we needed another striker, so that we could press high and make it hard for them to play from the back.
“We had chances on the counter attack but we needed to score. It’s like against Sporting, if we don’t score they can always score. I don’t think we deserved this result,” he stated.
City host Sporting in the Europa League on Thursday and need to overturn a 1-0 deficit, with their next league game against Chelsea on Monday night.
By Gareth McKnight