After taking a half-time lead through Jo, City were undone by two goals in as many second-half minutes from Gianni Zuiverloon and Simon Cox.
Mancini ended the contest with £100million worth of talent on the pitch, but it was not enough as Boaz Myhill turned away James Milner's last chance at a rescue mission.
The City boss might reflect on his decision to select six youngsters in his starting line-up.
However, with Chelsea due at Eastlands on Saturday lunchtime,
Mancini claimed he had no choice. "I don't regret making the changes," he said. "I have big problems at the moment and we couldn't take any risks.
"If I had more players available it would be a different team.
"But when you play like us and Chelsea, on Saturday at 12.45, the time to recover is very short. They would need minimum three days so to play would have been dangerous."
Source: PA
Source: PA