The Blues were hoping to warm up for Monday's FA Cup clash with West Ham by winning their 8th straight home game only to slump to a 1-0 defeat.
Pearce made 8 changes to City's starting XI, but coming into the side were experienced players like Danny Mills, Ben Thatcher and Sylvain Distin, and Pearce felt they under-performed.
Striker Ishmael Miller made his senior debut from the bench while fellow youngsters Stephen Ireland and Bradley Wright-Phillips started, but Pearce took little comfort from that.
"We were very average, right throughout the team," he said. "I don't think too many of us covered ourselves in glory. It was a poor performance and a little bit out of character with our recent home form.
"We will learn from it, maybe one or two of the youngsters will now know how difficult it is in the Premiership and that things do not come easily. We have copped a couple of injuries as well, which has not helped the situation.
"It's down to me now to pick them up and drive them forward to the next game, which a very important game for us.
"I don't take any cold comfort coming away from here and thinking, 'one or two youngsters got a game'. I will look at the performance and the result and class both as unacceptable, for me and the players."
Three players went off injured: Antoine Sibierski, Claudio Reyna and - most worryingly - Georgios Samaras. The in-form Greek striker was rested after going off at half-time in last Tuesday's 5th Round win over Villa, but was needed to replace Sibierski and then had to be substituted himself.